Java Tutorial—The Difference Between Int and Integer

First let’s talk about the difference between int and Integer:

int is the basic data type, and Integer is the wrapper class of int. Note: The type of the latter is "class". For example, using generics, List numList;

int has an initial value of 0, and integer is null.

Look at the specific example below:

package syswar.cc;

public class IntegerCompare {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Integer a1 = 2;
        Integer a2 = 2;

        Integer b1 = 150;
        Integer b2 = 150;

        Integer c1 = new Integer(2);
        Integer c2 = new Integer(2);

        Integer d1 = new Integer(150);
        Integer d2 = new Integer(150);

        System.out.println("a1==a2?" + (a1==a2));
        System.out.println("b1==b2?" + (b1==b2));
        System.out.println("c1==c2?" + (c1==c2));
        System.out.println("d1==d2?" + (d1==d2));
    }

}

Running result:

a1==a2?true
b1==b2?false
c1==c2?false
d1==d2?false>

Why is this result? Let's first compare the two groups a and b. When Integer is initialized, Integer object data is cached. The int values ​​corresponding to these Integer objects are in the byte range, that is, [-128,127].

When assigning an int value directly to Integer, if the value range is [-128,127], Integer directly takes the Integer object from the cache. Therefore, when the directly assigned int value is in [-128,127], the Integer object is the same object. .

The Integer object obtained through the new method is an object allocated directly from the heap. Therefore, no matter what the specific int value is, the result of the == judgment is false