I have a class and in that class I have this:
//some code
private int[] data = new int[3];
//some code
Then in my constructor:
public Date(){
data[0] = 0;
data[1] = 0;
data[2] = 0;
}
If I do this, everything is OK. Default data values are initialized but if I instead do this:
public Date(){
int[] data = {0,0,0};
}
It says:
Local variable hides a field
Why?
What's the best way to initialize an array inside the constructor?
private int[] data = new int[3];
This already initializes your array elements to 0. You don't need to repeat that again in the constructor.
In your constructor it should be:
data = new int[]{0, 0, 0};
You could either do:
public class Data {
private int[] data;
public Data() {
data = new int[]{0, 0, 0};
}
}
Which initializes data in the constructor, or:
public class Data {
private int[] data = new int[]{0, 0, 0};
public Data() {
// data already initialised
}
}
Which initializes data before the code in the constructor is executed.
public Data() throws Error { if OutOfMemoryError will be thrown.This is because, in the constructor, you declared a local variable with the same name as an attribute.
To allocate an integer array which all elements are initialized to zero, write this in the constructor:
data = new int[3];
To allocate an integer array which has other initial values, put this code in the constructor:
int[] temp = {2, 3, 7};
data = temp;
or:
data = new int[] {2, 3, 7};
why not simply
public Date(){
data = new int[]{0,0,0};
}
the reason you got the error is because int[] data = ... declares a new variable and hides the field data
however it should be noted that the contents of the array are already initialized to 0 (the default value of int)
in your constructor you are creating another int array:
public Date(){
int[] data = {0,0,0};
}
Try this:
data = {0,0,0};
NOTE: By the way you do NOT need to initialize your array elements if it is declared as an instance variable. Instance variables automatically get their default values, which for an integer array, the default values are all zeroes.
If you had locally declared array though they you would need to initialize each element.
The best way is not to write any initializing statements. This is because if you write
int a[]=new int[3] then by default, in Java all the values of array i.e. a[0], a[1] and a[2] are initialized to 0! Regarding the local variable hiding a field, post your entire code for us to come to conclusion.
Please remember that this will change the number of elements in the constructor. That is...
public class Test
{
int[] arr =new int[4];
int n = arr.length;
Test()
{
arr = new int[]{0,0,0,0,0,0,0};
n = arr.length;
}
}
In the Constructor, int[]{0,0,0,0,0,0,0} will compile successfully even though the limit is 4 because of the new keyword.
The final n value is 7.
dataafter"//some code"is having a scope of the entire class. while the variabledatain the constructor is having a scope inside the constructor. and once the constructor is done, the variable will be destroyed. And also thedatavariable inside constructor hides the variable by same name in the class. This justifies the errorLocal variable hides a field