Java initialize variable with null or not?

Question

I was wondering whether I should initialize class members in java with an initial value and then change that value to some other given value in the constructor, or should I avoid doing such a thing?

code example

public class Test {
    private int value = 5;

    public Test(int value) {
        this.value = value;
 }
}

Answer 1

If not specified,:

primitive bytes, shorts, ints, longs, floats and doubles are initialized to 0

booleans are initialized to false

Objects are initialized to null

Answer 2

If we are talking about class fields than all unset variables of

• primitive types are set to
  • 0 (numeric ones like int, long, double...)
  • \u0000 (char)
  • false (boolean).
• object types like String, Integer, or AnyOtherClass are set to null

so actually it doesn't matter if you set it explicitly, because

private int x;    
private Integer y;

is equivalent of

private int x = 0;    
private Integer y = null;

Answer 3

Java give value class variables, I mean they are initialized by JVM and you can use them. But you must to search their default values to use them correctly.

On the other hand, JVM does not initialize the local variables which is created in methods. So if you create any variable on methods you have to assign them to a value before use them.