2575

How do I declare and initialize an array in Java?

Improve this question
2
  • 45
    Before you post a new answer, consider there are already 25+ answers for this question. Please, make sure that your answer contributes information that is not among existing answers. Commented Feb 3, 2020 at 11:50
  • 2
    docs.oracle.com/javase/tutorial/java/nutsandbolts/arrays.html Commented Dec 22, 2020 at 9:03

31 Answers 31

Reset to default
1
2
3262

You can either use array declaration or array literal (but only when you declare and affect the variable right away, array literals cannot be used for re-assigning an array).

For primitive types:

int[] myIntArray = new int[3]; // each element of the array is initialised to 0
int[] myIntArray = {1, 2, 3};
int[] myIntArray = new int[]{1, 2, 3};

// Since Java 8. Doc of IntStream: https://docs.oracle.com/javase/8/docs/api/java/util/stream/IntStream.html

int [] myIntArray = IntStream.range(0, 100).toArray(); // From 0 to 99
int [] myIntArray = IntStream.rangeClosed(0, 100).toArray(); // From 0 to 100
int [] myIntArray = IntStream.of(12,25,36,85,28,96,47).toArray(); // The order is preserved.
int [] myIntArray = IntStream.of(12,25,36,85,28,96,47).sorted().toArray(); // Sort

For classes, for example String, it's the same:

String[] myStringArray = new String[3]; // each element is initialised to null
String[] myStringArray = {"a", "b", "c"};
String[] myStringArray = new String[]{"a", "b", "c"};

The third way of initializing is useful when you declare an array first and then initialize it, pass an array as a function argument, or return an array. The explicit type is required.

String[] myStringArray;
myStringArray = new String[]{"a", "b", "c"};
Improve this answer
Sign up to request clarification or add additional context in comments.

2 Comments

What's the purpose of having both the second and third way to do it?
@iamcreasy It looks like the second way doesn't work with return statements. return {1,2,3} gives an error, while return new int[]{1,2,3} works fine (assuming of course that your function returns an integer array).
336

There are two types of array.

One Dimensional Array

Syntax for default values:

int[] num = new int[5];

Or (less preferred)

int num[] = new int[5];

Syntax with values given (variable/field initialization):

int[] num = {1,2,3,4,5};

Or (less preferred)

int num[] = {1, 2, 3, 4, 5};

Note: For convenience int[] num is preferable because it clearly tells that you are talking here about array. Otherwise no difference. Not at all.

Multidimensional array

Declaration

int[][] num = new int[5][2];

Or

int num[][] = new int[5][2];

Or

int[] num[] = new int[5][2];

Initialization

 num[0][0]=1;
 num[0][1]=2;
 num[1][0]=1;
 num[1][1]=2;
 num[2][0]=1;
 num[2][1]=2;
 num[3][0]=1;
 num[3][1]=2;
 num[4][0]=1;
 num[4][1]=2;

Or

 int[][] num={ {1,2}, {1,2}, {1,2}, {1,2}, {1,2} };

Ragged Array (or Non-rectangular Array)

 int[][] num = new int[5][];
 num[0] = new int[1];
 num[1] = new int[5];
 num[2] = new int[2];
 num[3] = new int[3];

So here we are defining columns explicitly.
Another Way: 

int[][] num={ {1}, {1,2}, {1,2,3,4,5}, {1,2}, {1,2,3} };

For Accessing:

for (int i=0; i<(num.length); i++ ) {
    for (int j=0;j<num[i].length;j++)
        System.out.println(num[i][j]);
}

Alternatively:

for (int[] a : num) {
  for (int i : a) {
    System.out.println(i);
  }
}

Ragged arrays are multidimensional arrays.
For explanation see multidimensional array detail at the official java tutorials

Improve this answer

4 Comments

Won't the first one lead to a null/empty array, instead of array with default values?
I agree on that point, and we can add one more feature, we can change the size dynamically.
I might argue with you on the point that a multidimensional array is a different "type" of array. It's simply a term used to describe an array that happens to contain other arrays. Both the outer arrays and the inner arrays (and those in between, if they exist) are just regular arrays.
Perhaps worth noting that the second (less-preferred) form stems from C/C++. This might be the reason why it is supported in Java.
141 
Type[] variableName = new Type[capacity];

Type[] variableName = {comma-delimited values};



Type variableName[] = new Type[capacity]; 

Type variableName[] = {comma-delimited values};

is also valid, but I prefer the brackets after the type, because it's easier to see that the variable's type is actually an array.

Improve this answer

4 Comments

I agree on that point. The type of the variable is not "TYPE", but actually a TYPE[], so it makes sense to write it that way for me.
Google style suggest this too.
Note that int[] a, b; will not be the same as int a[], b;, a mistake easy to make if you use the latter form.
Updated Google style link: google.github.io/styleguide/javaguide.html#s4.8.3-arrays
45

There are various ways in which you can declare an array in Java:

float floatArray[]; // Initialize later
int[] integerArray = new int[10];
String[] array = new String[] {"a", "b"};

You can find more information in the Sun tutorial site and the JavaDoc.

Improve this answer

1 Comment

This answer fails to properly address the question: "How do I declare and initialize an array in Java?" Other answers here show that it is simple to initialize float and int arrays when they are declared. There is no need to "Initialize later".
35

I find it is helpful if you understand each part:

Type[] name = new Type[5];

Type[] is the type of the variable called name ("name" is called the identifier). The literal "Type" is the base type, and the brackets mean this is the array type of that base. Array types are in turn types of their own, which allows you to make multidimensional arrays like Type[][] (the array type of Type[]). The keyword new says to allocate memory for the new array. The number between the bracket says how large the new array will be and how much memory to allocate. For instance, if Java knows that the base type Type takes 32 bytes, and you want an array of size 5, it needs to internally allocate 32 * 5 = 160 bytes.

You can also create arrays with the values already there, such as

int[] name = {1, 2, 3, 4, 5};

which not only creates the empty space but fills it with those values. Java can tell that the primitives are integers and that there are 5 of them, so the size of the array can be determined implicitly.

Improve this answer

1 Comment

So it is not necessary to include int[] name = new int[5] ?
35

The following shows the declaration of an array, but the array is not initialized:

int[] myIntArray = new int[3];

The following shows the declaration as well as initialization of the array:

int[] myIntArray = {1,2,3};

Now, the following also shows the declaration as well as initialization of the array:

int[] myIntArray = new int[]{1,2,3};

But this third one shows the property of anonymous array-object creation which is pointed by a reference variable "myIntArray", so if we write just "new int[]{1,2,3};" then this is how anonymous array-object can be created.

If we just write:

int[] myIntArray;

this is not declaration of array, but the following statement makes the above declaration complete:

myIntArray=new int[3];
Improve this answer

3 Comments

There is absolutely no difference between the second and third approaches, other than that the second approach only works when you're also declaring a variable. It's not clear what you mean by "shows the property of anonymous array-object creation" but they really are equivalent pieces of code.
Also, the first snippet does initialize the array - it is guaranteed to have the value 0 for every array element.
Is there really no difference between the second and the third one approaches?
30

Alternatively,

// Either method works
String arrayName[] = new String[10];
String[] arrayName = new String[10];

That declares an array called arrayName of size 10 (you have elements 0 through 9 to use).

Improve this answer

2 Comments

What is the standard for which to use? I've only just discovered the former, and I find it horrifically misleading :|
For what it's worth my prof said that the second way is more typical in Java and that it better conveys what is going on; as an array related to the type the variable was cast as.
28

Also, in case you want something more dynamic there is the List interface. This will not perform as well, but is more flexible:

List<String> listOfString = new ArrayList<String>();

listOfString.add("foo");
listOfString.add("bar");

String value = listOfString.get(0);
assertEquals( value, "foo" );
Improve this answer

2 Comments

what is the "<>" called in the list that you created ?
@CyprUS List is a generic class, it has a type as a parameter, enclosed in <>. That helps because you only need to define a generic type once and you can then use it with multiple different types. For a more detailed explanation look at docs.oracle.com/javase/tutorial/java/generics/types.html
18

There are two main ways to make an array:

This one, for an empty array:

int[] array = new int[n]; // "n" being the number of spaces to allocate in the array

And this one, for an initialized array:

int[] array = {1,2,3,4 ...};

You can also make multidimensional arrays, like this:

int[][] array2d = new int[x][y]; // "x" and "y" specify the dimensions
int[][] array2d = { {1,2,3 ...}, {4,5,6 ...} ...};
Improve this answer

Comments

18

In Java 8

Using Arrays.setAll (similar to Arrays.fill, but takes the generator function, which accepts an index and produces the desired value for that position, which gives more flexibility):

int[] a = new int[5];
Arrays.setAll(a, index -> index + 1);

Out: [1, 2, 3, 4, 5]

In Java 9

Using different IntStream.iterate and IntStream.takeWhile methods:

int[] a = IntStream.iterate(10, x -> x <= 100, x -> x + 10).toArray();

Out: [10, 20, 30, 40, 50, 60, 70, 80, 90, 100]


int[] b = IntStream.iterate(0, x -> x + 1).takeWhile(x -> x < 10).toArray();

Out: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

In Java 10

Using the Local Variable Type Inference:

var letters = new String[]{"A", "B", "C"};
Improve this answer

Comments

14

Take the primitive type int for example. There are several ways to declare and int array:

int[] i = new int[capacity];
int[] i = new int[] {value1, value2, value3, etc};
int[] i = {value1, value2, value3, etc};

where in all of these, you can use int i[] instead of int[] i.

With reflection, you can use (Type[]) Array.newInstance(Type.class, capacity);

Note that in method parameters, ... indicates variable arguments. Essentially, any number of parameters is fine. It's easier to explain with code:

public static void varargs(int fixed1, String fixed2, int... varargs) {...}
...
varargs(0, "", 100); // fixed1 = 0, fixed2 = "", varargs = {100}
varargs(0, "", 100, 200); // fixed1 = 0, fixed2 = "", varargs = {100, 200};

Inside the method, varargs is treated as a normal int[]. Type... can only be used in method parameters, so int... i = new int[] {} will not compile.

Note that when passing an int[] to a method (or any other Type[]), you cannot use the third way. In the statement int[] i = *{a, b, c, d, etc}*, the compiler assumes that the {...} means an int[]. But that is because you are declaring a variable. When passing an array to a method, the declaration must either be new Type[capacity] or new Type[] {...}.

Multidimensional Arrays

Multidimensional arrays are much harder to deal with. Essentially, a 2D array is an array of arrays. int[][] means an array of int[]s. The key is that if an int[][] is declared as int[x][y], the maximum index is i[x-1][y-1]. Essentially, a rectangular int[3][5] is:

[0, 0] [1, 0] [2, 0]
[0, 1] [1, 1] [2, 1]
[0, 2] [1, 2] [2, 2]
[0, 3] [1, 3] [2, 3]
[0, 4] [1, 4] [2, 4]
Improve this answer

Comments

13

In Java 8 you can use something like this.

String[] strs = IntStream.range(0, 15)  // 15 is the size
    .mapToObj(i -> Integer.toString(i))
    .toArray(String[]::new);
Improve this answer

Comments

12

If you want to create arrays using reflections then you can do like this:

int size = 3;
int[] intArray = (int[]) Array.newInstance(int.class, size );
Improve this answer

2 Comments

Why would you want to create an array that way?
your question applies to all variant of provided answers in this section. really question might be is why language having variety of declarations for one thing? and the answer what I assume can be that all variants helps us in several situations and hence language is supporting us to perform things as required.
11

Array is a sequential list of items

int item = value;

int [] one_dimensional_array = { value, value, value, .., value };

int [][] two_dimensional_array =
{
  { value, value, value, .. value },
  { value, value, value, .. value },
    ..     ..     ..        ..
  { value, value, value, .. value }
};

If it's an object, then it's the same concept

Object item = new Object();

Object [] one_dimensional_array = { new Object(), new Object(), .. new Object() };

Object [][] two_dimensional_array =
{
  { new Object(), new Object(), .. new Object() },
  { new Object(), new Object(), .. new Object() },
    ..            ..               ..
  { new Object(), new Object(), .. new Object() }
};

In case of objects, you need to either assign it to null to initialize them using new Type(..), classes like String and Integer are special cases that will be handled as following

String [] a = { "hello", "world" };
// is equivalent to
String [] a = { new String({'h','e','l','l','o'}), new String({'w','o','r','l','d'}) };

Integer [] b = { 1234, 5678 };
// is equivalent to
Integer [] b = { new Integer(1234), new Integer(5678) };

In general you can create arrays that's M dimensional

int [][]..[] array =
//  ^ M times [] brackets

    {{..{
//  ^ M times { bracket

//            this is array[0][0]..[0]
//                         ^ M times [0]

    }}..}
//  ^ M times } bracket
;

It's worthy to note that creating an M dimensional array is expensive in terms of Space. Since when you create an M dimensional array with N on all the dimensions, The total size of the array is bigger than N^M, since each array has a reference, and at the M-dimension there is an (M-1)-dimensional array of references. The total size is as following

Space = N^M + N^(M-1) + N^(M-2) + .. + N^0
//      ^                              ^ array reference
//      ^ actual data
Improve this answer

Comments

11

Declaration

One Dimensional Array

int[] nums1; // best practice
int []nums2;
int nums3[];

Multidimensional array

int[][] nums1; // best practice
int [][]nums2;
int[] []nums3;
int[] nums4[];
int nums5[][];

Declaration and Initialization

One Dimensional Array

With default values

int[] nums = new int[3]; // [0, 0, 0]

Object[] objects = new Object[3]; // [null, null, null]

With array literal

int[] nums1 = {1, 2, 3};
int[] nums2 = new int[]{1, 2, 3};

Object[] objects1 = {new Object(), new Object(), new Object()};
Object[] objects2 = new Object[]{new Object(), new Object(), new Object()};

With loop for

int[] nums = new int[3];
for (int i = 0; i < nums.length; i++) {
    nums[i] = i; // can contain any YOUR filling strategy
}

Object[] objects = new Object[3];
for (int i = 0; i < objects.length; i++) {
    objects[i] = new Object(); // can contain any YOUR filling strategy
}

With loop for and Random

int[] nums = new int[10];
Random random = new Random();
for (int i = 0; i < nums.length; i++) {
    nums[i] = random.nextInt(10); // random int from 0 to 9
}

With Stream (since Java 8)

int[] nums1 = IntStream.range(0, 3)
                       .toArray(); // [0, 1, 2]
int[] nums2 = IntStream.rangeClosed(0, 3)
                       .toArray(); // [0, 1, 2, 3]
int[] nums3 = IntStream.of(10, 11, 12, 13)
                       .toArray(); // [10, 11, 12, 13]
int[] nums4 = IntStream.of(12, 11, 13, 10)
                       .sorted()
                       .toArray(); // [10, 11, 12, 13]
int[] nums5 = IntStream.iterate(0, x -> x <= 3, x -> x + 1)
                       .toArray(); // [0, 1, 2, 3]
int[] nums6 = IntStream.iterate(0, x -> x + 1)
                       .takeWhile(x -> x < 3)
                       .toArray(); // [0, 1, 2]

int size = 3;
Object[] objects1 = IntStream.range(0, size)
        .mapToObj(i -> new Object()) // can contain any YOUR filling strategy
        .toArray(Object[]::new);

Object[] objects2 = Stream.generate(() -> new Object()) // can contain any YOUR filling strategy
        .limit(size)
        .toArray(Object[]::new);

With Random and Stream (since Java 8)

int size = 3;
int randomNumberOrigin = -10;
int randomNumberBound = 10
int[] nums = new Random().ints(size, randomNumberOrigin, randomNumberBound).toArray();

Multidimensional array

With default value

int[][] nums = new int[3][3]; // [[0, 0, 0], [0, 0, 0], [0, 0, 0]]

Object[][] objects = new Object[3][3]; // [[null, null, null], [null, null, null], [null, null, null]]

With array literal

int[][] nums1 = {
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
};
int[][] nums2 = new int[][]{
        {1, 2, 3},
        {4, 5, 6},
        {7, 8, 9}
};

Object[][] objects1 = {
        {new Object(), new Object(), new Object()},
        {new Object(), new Object(), new Object()},
        {new Object(), new Object(), new Object()}
};
Object[][] objects2 = new Object[][]{
        {new Object(), new Object(), new Object()},
        {new Object(), new Object(), new Object()},
        {new Object(), new Object(), new Object()}
};

With loop for

int[][] nums = new int[3][3];
for (int i = 0; i < nums.length; i++) {
    for (int j = 0; j < nums[i].length; i++) {
        nums[i][j] = i + j; // can contain any YOUR filling strategy
    }
}

Object[][] objects = new Object[3][3];
for (int i = 0; i < objects.length; i++) {
    for (int j = 0; j < nums[i].length; i++) {
        objects[i][j] = new Object(); // can contain any YOUR filling strategy
    }
}
Improve this answer

Comments

11

Declaring an array of object references:

class Animal {}

class Horse extends Animal {
    public static void main(String[] args) {

        /*
         * Array of Animal can hold Animal and Horse (all subtypes of Animal allowed)
         */
        Animal[] a1 = new Animal[10];
        a1[0] = new Animal();
        a1[1] = new Horse();

        /*
         * Array of Animal can hold Animal and Horse and all subtype of Horse
         */
        Animal[] a2 = new Horse[10];
        a2[0] = new Animal(); //Throws ArrayStoreException at runtime. no compilation error.
        a2[1] = new Horse();

        /*
         * Array of Horse can hold only Horse and its subtype (if any) and not
           allowed supertype of Horse nor other subtype of Animal.
         */
        Horse[] h1 = new Horse[10];
        h1[0] = new Animal(); // Not allowed
        h1[1] = new Horse();

        /*
         * This can not be declared.
         */
        Horse[] h2 = new Animal[10]; // Not allowed
    }
}
Improve this answer

2 Comments

incorrect comment "Array of Animal can hold Animal" and example - a2[0] = new Animal(); throws ArrayStoreException - a2 even if declared as Animal[] but initialized with new Horse[10] will not be able to hold an instance of Animal or any subtype of Animal that is not an instance of Horse or a subtype of Horse -- an array knows its element type at runtime (error if doing like a2[0] = new Animal() or a2[0] = new Cat())
Thanks @user85421 , updated comment a2[0] = new Animal(); //Throws ArrayStoreException at runtime. no compilation error.
10

If by "array" you meant using java.util.Arrays, you can do it with:

List<String> number = Arrays.asList("1", "2", "3");

// Out: ["1", "2", "3"]

This one is pretty simple and straightforward to create a List. (What is difference between List and Array?) Now if you really wanted an Array you may still get one using:

String[] numberArray = Arrays.asList("1", "2", "3").toArray(new String[0]);
Improve this answer

3 Comments

A list is not an array
Sometime people mean arrays, when they want a list.
And sometimes the y do not understand the difference between those two, so a good answer would at least mention that a List object is similar to an array type instance, but not the same.
9

Declare and initialize for Java 8 and later. Create a simple integer array:

int [] a1 = IntStream.range(1, 20).toArray();
System.out.println(Arrays.toString(a1));
// Output: [1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19]

Create a random array for integers between [-50, 50] and for doubles [0, 1E17]:

int [] a2 = new Random().ints(15, -50, 50).toArray();
double [] a3 = new Random().doubles(5, 0, 1e17).toArray();

Power-of-two sequence:

double [] a4 = LongStream.range(0, 7).mapToDouble(i -> Math.pow(2, i)).toArray();
System.out.println(Arrays.toString(a4));
// Output: [1.0, 2.0, 4.0, 8.0, 16.0, 32.0, 64.0]

For String[] you must specify a constructor:

String [] a5 = Stream.generate(()->"I will not squeak chalk").limit(5).toArray(String[]::new);
System.out.println(Arrays.toString(a5));

Multidimensional arrays:

String [][] a6 = List.of(new String[]{"a", "b", "c"} , new String[]{"d", "e", "f", "g"})
    .toArray(new String[0][]);
System.out.println(Arrays.deepToString(a6));
// Output: [[a, b, c], [d, e, f, g]]
Improve this answer

2 Comments

Are -50 and/or +50 actually included? That is, is the internal open at one or both ends?
-50 is included and +50 is excluded. This information from java api "given origin (inclusive) and bound (exclusive)." I use interval declaration from wiki . So I think it will be more correct [-50, 50)
7

For creating arrays of class Objects you can use the java.util.ArrayList. to define an array:

public ArrayList<ClassName> arrayName;
arrayName = new ArrayList<ClassName>();

Assign values to the array:

arrayName.add(new ClassName(class parameters go here);

Read from the array:

ClassName variableName = arrayName.get(index);

Note:

variableName is a reference to the array meaning that manipulating variableName will manipulate arrayName

for loops:

//repeats for every value in the array
for (ClassName variableName : arrayName){
}
//Note that using this for loop prevents you from editing arrayName

for loop that allows you to edit arrayName (conventional for loop):

for (int i = 0; i < arrayName.size(); i++){
    //manipulate array here
}
Improve this answer

Comments

7 
int[] x = new int[enter the size of array here];

Example:

int[] x = new int[10];

Or

int[] x = {enter the elements of array here];

Example:

int[] x = {10, 65, 40, 5, 48, 31};
Improve this answer

Comments

7

There are a lot of answers here. I am adding a few tricky ways to create arrays (from an exam point of view it's good to know this)

  1. Declare and define an array

     int intArray[] = new int[3];

    This will create an array of length 3. As it holds a primitive type, int, all values are set to 0 by default. For example,

     intArray[2]; // Will return 0

  2. Using box brackets [] before the variable name

     int[] intArray = new int[3];
 intArray[0] = 1;  // Array content is now {1, 0, 0}

  3. Initialise and provide data to the array

     int[] intArray = new int[]{1, 2, 3};

    This time there isn't any need to mention the size in the box bracket. Even a simple variant of this is:

     int[] intArray = {1, 2, 3, 4};

  4. An array of length 0

     int[] intArray = new int[0];
 int length = intArray.length; // Will return length 0

**Similar for multi-dimensional arrays**

 int intArray[][] = new int[2][3];
 // This will create an array of length 2 and
 //each element contains another array of length 3.
 // { {0,0,0},{0,0,0} }
 int lenght1 = intArray.length; // Will return 2
 int length2 = intArray[0].length; // Will return 3

Using box brackets before the variable:

    int[][] intArray = new int[2][3];

It's absolutely fine if you put one box bracket at the end:

    int[] intArray [] = new int[2][4];
    int[] intArray[][] = new int[2][3][4]

Some examples

    int [] intArray [] = new int[][] {{1,2,3},{4,5,6}};
    int [] intArray1 [] = new int[][] {new int[] {1,2,3}, new int [] {4,5,6}};
    int [] intArray2 [] = new int[][] {new int[] {1,2,3},{4,5,6}}
    // All the 3 arrays assignments are valid
    // Array looks like {{1,2,3},{4,5,6}}

It's not mandatory that each inner element is of the same size.

    int [][] intArray = new int[2][];
    intArray[0] = new int[]{1,2,3};
    intArray[1] = new int[]{4,5};
    //array looks like {{1,2,3},{4,5}}

    int[][] intArray = new int[][2] ; // This won't compile. Keep this in mind.

You have to make sure if you are using the above syntax, that the forward direction you have to specify the values in box brackets. Else it won't compile. Some examples:

    int [][][] intArray = new int[1][][];
    int [][][] intArray = new int[1][2][];
    int [][][] intArray = new int[1][2][3];

Another important feature is covariant

    Number[] numArray = {1,2,3,4};   // java.lang.Number
    numArray[0] = new Float(1.5f);   // java.lang.Float
    numArray[1] = new Integer(1);    // java.lang.Integer
   // You can store a subclass object in an array that is declared
   // to be of the type of its superclass.
   // Here 'Number' is the superclass for both Float and Integer.

   Number num[] = new Float[5]; // This is also valid

IMPORTANT: For referenced types, the default value stored in the array is null.

Improve this answer

5 Comments

maybe important to note that multi-dimensional arrays are actually arrays of arrays, so int[][] array = new int[2][]; is creating an array with 2 positions (that can hold an int[] array each) initialized with null (e.g. array[1] returns null; array[1][0] throws a NullPointerException)
Primitive Java (int) cannot be null @user85421
sure; but where did I say that a primitive can be null? I wrote that an int[], that is an array of primitives (or whatever,) which is a normal instance (subclass of Object) can be null -- you should have tried, maybe the test case I provided, yourself, less than 2 Minutes: ideone.com/o91j7e ( or, even simpler, just test int[] subArray = null; )
and, by the way, re-reading your answer: intArray[0] = {1,2,3}; is not valid in Java ! (the short form is only accepted in variable declarations)
if you have doubt just not read, copy that to yout intelliJ or any editor and try int [][] intArray = new int[2][]; intArray[0] = new int[]{1,2,3}; intArray[1] = new int[]{4,5}; '''' its all working for me.
6

An array has two basic types.

Static Array: Fixed size array (its size should be declared at the start and can not be changed later)

Dynamic Array: No size limit is considered for this. (Pure dynamic arrays do not exist in Java. Instead, List is most encouraged.)

To declare a static array of Integer, string, float, etc., use the below declaration and initialization statements.

int[] intArray = new int[10];
String[] intArray = new int[10];
float[] intArray = new int[10];

// Here you have 10 index starting from 0 to 9

To use dynamic features, you have to use List... List is pure dynamic Array and there is no need to declare size at beginning. Below is the proper way to declare a list in Java -

ArrayList<String> myArray = new ArrayList<String>();
myArray.add("Value 1: something");
myArray.add("Value 2: something more");
Improve this answer

1 Comment

Thank you @Matheus for improving my answers. I would request you to upvote this, so this can reach more users.
5

An array can contain primitives data types as well as objects of a class depending on the definition of the array. In case of primitives data types, the actual values are stored in contiguous memory locations. In case of objects of a class, the actual objects are stored in the heap segment.


One-Dimensional Arrays:

The general form of a one-dimensional array declaration is

type var-name[];
OR
type[] var-name;

Instantiating an Array in Java

var-name = new type [size];

For example,

int intArray[];  // Declaring an array
intArray = new int[20];  // Allocating memory to the array

// The below line is equal to line1 + line2
int[] intArray = new int[20]; // Combining both statements in one
int[] intArray = new int[]{ 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 };

// Accessing the elements of the specified array
for (int i = 0; i < intArray.length; i++)
    System.out.println("Element at index " + i + ": "+ intArray[i]);

Ref: Arrays in Java

Improve this answer

1 Comment

BTW writing int[] array is preferred over int array[]
4

Another way to declare and initialize ArrayList:

private List<String> list = new ArrayList<String>(){{
    add("e1");
    add("e2");
}};
Improve this answer

1 Comment

array != ArrayList -- and -- double { is a bad pattern, it is actually creating an anonymous class with no additional functionality (but putting two values into the list); better ways Arrays.asList() and bit newer List.of()
4

With local variable type inference you only have to specify the type once:

var values = new int[] { 1, 2, 3 };

Or

int[] values = { 1, 2, 3 }
Improve this answer

1 Comment

@CameronHudson Java 10 has var openjdk.java.net/jeps/286
2

Sometimes I use this for initializing String arrays:

private static final String[] PROPS = "lastStart,storetime,tstore".split(",");

It reduces the quoting clutter at the cost of a more expensive initialization.

Improve this answer

Comments

1

Declare Array: int[] arr;

Initialize Array: int[] arr = new int[10]; 10 represents the number of elements allowed in the array

Declare Multidimensional Array: int[][] arr;

Initialize Multidimensional Array: int[][] arr = new int[10][17]; 10 rows and 17 columns and 170 elements because 10 times 17 is 170.

Initializing an array means specifying the size of it.

Improve this answer

Comments

1 
package com.examplehub.basics;

import java.util.Arrays;

public class Array {

    public static void main(String[] args) {
        int[] numbers = {1, 2, 3, 4, 5};

        /*
         * numbers[0] = 1
         * numbers[1] = 2
         * numbers[2] = 3
         * numbers[3] = 4
         * numbers[4] = 5
         */
        System.out.println("numbers[0] = " + numbers[0]);
        System.out.println("numbers[1] = " + numbers[1]);
        System.out.println("numbers[2] = " + numbers[2]);
        System.out.println("numbers[3] = " + numbers[3]);
        System.out.println("numbers[4] = " + numbers[4]);

        /*
         * Array index is out of bounds
         */
        //System.out.println(numbers[-1]);
        //System.out.println(numbers[5]);


        /*
         * numbers[0] = 1
         * numbers[1] = 2
         * numbers[2] = 3
         * numbers[3] = 4
         * numbers[4] = 5
         */
        for (int i = 0; i < 5; i++) {
            System.out.println("numbers[" + i + "] = " + numbers[i]);
        }

        /*
         * Length of numbers = 5
         */
        System.out.println("length of numbers = " + numbers.length);

        /*
         * numbers[0] = 1
         * numbers[1] = 2
         * numbers[2] = 3
         * numbers[3] = 4
         * numbers[4] = 5
         */
        for (int i = 0; i < numbers.length; i++) {
            System.out.println("numbers[" + i + "] = " + numbers[i]);
        }

        /*
         * numbers[4] = 5
         * numbers[3] = 4
         * numbers[2] = 3
         * numbers[1] = 2
         * numbers[0] = 1
         */
        for (int i = numbers.length - 1; i >= 0; i--) {
            System.out.println("numbers[" + i + "] = " + numbers[i]);
        }

        /*
         * 12345
         */
        for (int number : numbers) {
            System.out.print(number);
        }
        System.out.println();

        /*
         * [1, 2, 3, 4, 5]
         */
        System.out.println(Arrays.toString(numbers));



        String[] company = {"Google", "Facebook", "Amazon", "Microsoft"};

        /*
         * company[0] = Google
         * company[1] = Facebook
         * company[2] = Amazon
         * company[3] = Microsoft
         */
        for (int i = 0; i < company.length; i++) {
            System.out.println("company[" + i + "] = " + company[i]);
        }

        /*
         * Google
         * Facebook
         * Amazon
         * Microsoft
         */
        for (String c : company) {
            System.out.println(c);
        }

        /*
         * [Google, Facebook, Amazon, Microsoft]
         */
        System.out.println(Arrays.toString(company));

        int[][] twoDimensionalNumbers = {
                {1, 2, 3},
                {4, 5, 6, 7},
                {8, 9},
                {10, 11, 12, 13, 14, 15}
        };

        /*
         * total rows  = 4
         */
        System.out.println("total rows  = " + twoDimensionalNumbers.length);

        /*
         * row 0 length = 3
         * row 1 length = 4
         * row 2 length = 2
         * row 3 length = 6
         */
        for (int i = 0; i < twoDimensionalNumbers.length; i++) {
            System.out.println("row " + i + " length = " + twoDimensionalNumbers[i].length);
        }

        /*
         * row 0 = 1 2 3
         * row 1 = 4 5 6 7
         * row 2 = 8 9
         * row 3 = 10 11 12 13 14 15
         */
        for (int i = 0; i < twoDimensionalNumbers.length; i++) {
            System.out.print("row " + i + " = ");
            for (int j = 0; j < twoDimensionalNumbers[i].length; j++) {
                System.out.print(twoDimensionalNumbers[i][j] + " ");
            }
            System.out.println();
        }

        /*
         * row 0 = [1, 2, 3]
         * row 1 = [4, 5, 6, 7]
         * row 2 = [8, 9]
         * row 3 = [10, 11, 12, 13, 14, 15]
         */
        for (int i = 0; i < twoDimensionalNumbers.length; i++) {
            System.out.println("row " + i + " = " + Arrays.toString(twoDimensionalNumbers[i]));
        }

        /*
         * 1 2 3
         * 4 5 6 7
         * 8 9
         * 10 11 12 13 14 15
         */
        for (int[] ints : twoDimensionalNumbers) {
            for (int num : ints) {
                System.out.print(num + " ");
            }
            System.out.println();
        }

        /*
         * [1, 2, 3]
         * [4, 5, 6, 7]
         * [8, 9]
         * [10, 11, 12, 13, 14, 15]
         */
        for (int[] ints : twoDimensionalNumbers) {
            System.out.println(Arrays.toString(ints));
        }


        int length = 5;
        int[] array = new int[length];
        for (int i = 0; i < 5; i++) {
            array[i] = i + 1;
        }

        /*
         * [1, 2, 3, 4, 5]
         */
        System.out.println(Arrays.toString(array));

    }
}

Source from examplehub/java

Improve this answer

1 Comment

An explanation would be in order.
1

One another full example with a movies class:

public class A {

    public static void main(String[] args) {

        class Movie {

            String movieName;
            String genre;
            String movieType;
            String year;
            String ageRating;
            String rating;

            public Movie(String [] str)
            {
                this.movieName = str[0];
                this.genre = str[1];
                this.movieType = str[2];
                this.year = str[3];
                this.ageRating = str[4];
                this.rating = str[5];
            }
        }

        String [] movieDetailArr = {"Inception", "Thriller", "MovieType", "2010", "13+", "10/10"};

        Movie mv = new Movie(movieDetailArr);

        System.out.println("Movie Name: "+ mv.movieName);
        System.out.println("Movie genre: "+ mv.genre);
        System.out.println("Movie type: "+ mv.movieType);
        System.out.println("Movie year: "+ mv.year);
        System.out.println("Movie age : "+ mv.ageRating);
        System.out.println("Movie  rating: "+ mv.rating);
    }
}
Improve this answer

Comments

1

for initializing with default value other than 0:

var arr = new int[1000];
Arrays.fill(arr, 1);
Improve this answer

Comments

1
2

Start asking to get answers

Find the answer to your question by asking.

Ask question

Explore related questions

See similar questions with these tags.