Can I insert array to array and read it afterwards in Java? Something like this:
ArrayList<Integer> array = new ArrayList<>();
array.add([1,4,5]);
array.add([3,7,2]);
Array:
{ [1,4,5], [3,7,2] }
And read like:
print(array[0][1]); //prints 4
Thanks.
You could write ArrayList<int[]> and pass values like .add(new int[]{...}).
For example,
List<int[]> list = new ArrayList<>();
list.add(new int[]{1, 2, 3});
To print values out you should get an int[] array firstly by get(int index) and then get a value from this array by [index]:
System.out.print(list.get(0)[0]); // prints 1
About the mess in the comments.
List or List<Object> anywhere.int[] is an array, therefore it is a reference type and can be used as a generic parameter.int is a primitive which doesn't work/use with generics. Consider its wrapper class - Integer.<> above. Why? To prevent "boilerplate code".In Java SE 7 and later, you can replace the type arguments required to invoke the constructor of a generic class with an empty set of type arguments (
<>) as long as the compiler can determine, or infer, the type arguments from the context. This pair of angle brackets,<>, is informally called the diamond.
List<int[]> list = new ArrayList<>();
List<int[]> list = new ArrayList<int[]>();is equivalent to the previous
int is a primitive type, not a raw type.
<> is ok here.to quickly fill an arrayList with fewest lines of code :
Integer[] numArray = {1, 2, 3, 4, 5, 0, 9, 8, 7, 6};
List<Integer> numList = new ArrayList<>(Arrays.asList(numArray));
You can add integer arrays to an arraylist, but then the arraylist must be defined as:
List<int[]> list = new ArrayList<int[]>();
In Fact a more generic version would be:
List<Object> list = new ArrayList<Object>();
The array.add([1,4,5]); is implemented correctly as
list.add(new int[]{1,4,5});
The print(array[1][2]); is implemented correctly as:
System.out.println(((int [])list.get(1))[2]);
ArrayList is List type.
If you want to create 2d array (array inside array)
int[][] a = new int[][]{{1,4,5},{3,7,2}};
System.out.println(a[0][1]);
You want to use ArrayList of ArrayLists
ArrayList<ArrayList<Integer>> intArrays = new ArrayList<ArrayList<Integer>>();
//rows
for(int i =0;i<4;i++)
{
intArrays.add(new ArrayList<Integer>());
//cols
for(int j=0;j<4;j++)
{
intArrays.get(i).add(j);
}
}
//rows
for(int i =0;i<4;i++)
{
//cols
for(int j=0;j<4;j++)
{
System.out.print(intArrays.get(i).get(j));
}
System.out.println();
}
This has been tested and is working.
int[] ar = {10, 20, 20, 10, 10, 30, 50, 10, 20};
ArrayList<Integer> list = new ArrayList<>();
for(int i:ar){
list.add(new Integer(i));
}
System.out.println(list.toString());
// prints : [10, 20, 20, 10, 10, 30, 50, 10, 20]
