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
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

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