What is the difference between (Integer)y and new Integer(y) in java?

Question

What is the difference between the following:

Integer in = (Integer)y;

and

Integer in = new Integer(y);

I want to convert int type to Integer type and vice versa. Here is my code for doing that:

public class CompareToDemo {

  public static void main(String[] args) {
    // Integer x=5;
    int y=25;

    System.out.println(y+" this is  int variable");

    Integer in = (Integer)y;

    //Integer in = new Integer(y);

    if(in instanceof Integer){
      System.out.println(in +" this is Integer variable");
    }
  }
}

Answer 1

If all you want to do is to convert an int primitive to an Integer object, you have four options

   Integer in = (Integer)y;         // 1 explicit cast
   Integer in = y;                  // 2 implicit cast (autoboxing)
   Integer in = new Integer(y);     // 3 explicit constructor
   Integer in = Integer.valueOf(y); // 4 static factory method

The most preferable way here is 2 (autoboxing). The explicit constructor (3) is the less preferable, as it might have some small performance hit.

Also, they are not strictly equivalent. Consider:

public static void main(String[] args) {
    int x = 25;
    Integer a = new Integer(x);
    Integer b = new Integer(x);
    System.out.println(a == b);     // false
    Integer c = Integer.valueOf(x);
    Integer d = Integer.valueOf(x);
    System.out.println(c == d);     // true
    Integer e = (Integer)x;
    Integer f = (Integer)x;
    System.out.println(e == f);     // true
}

This is because small integers are cached (details here).