public class Test1 {

    /**

     * @param args

     */

    public static void main(String[] args){

        int a = 1000, b = 1000;

        System.out.println(a == b);

        Integer c = 1000, d = 1000;

        System.out.println(c==d);

        Integer e = 100, f = 100;

        System.out.println(e == f);

    }

}

运行结果：

true

false

true

结果分析：

查看Test1.class文件如下：

public class Test1 extends java.lang.Object{

public Test1();

  Code:

   0:   aload_0

   1:   invokespecial   #1; //Method java/lang/Object."<init>":()V

   4:   return

public static void main(java.lang.String[]);

  Code:

   0:   sipush  1000

   3:   istore_1

   4:   sipush  1000

   7:   istore_2

   8:   getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;

   11:  iload_1

   12:  iload_2

   13:  if_icmpne       20

   16:  iconst_1

   17:  goto    21

   20:  iconst_0

   21:  invokevirtual   #3; //Method java/io/PrintStream.println:(Z)V

   24:  sipush  1000

   27:  invokestatic    #4; //Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;

   30:  astore_3

   31:  sipush  1000

   34:  invokestatic    #4; //Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;

   37:  astore  4

   39:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;

   42:  aload_3

   43:  aload   4

   45:  if_acmpne       52

   48:  iconst_1

   49:  goto    53

   52:  iconst_0

   53:  invokevirtual   #3; //Method java/io/PrintStream.println:(Z)V

   56:  bipush  100

   58:  invokestatic    #4; //Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;

   61:  astore  5

   63:  bipush  100

   65:  invokestatic    #4; //Method java/lang/Integer.valueOf:(I)Ljava/lang/Integer;

   68:  astore  6

   70:  getstatic       #2; //Field java/lang/System.out:Ljava/io/PrintStream;

   73:  aload   5

   75:  aload   6

   77:  if_acmpne       84

   80:  iconst_1

   81:  goto    85

   84:  iconst_0

   85:  invokevirtual   #3; //Method java/io/PrintStream.println:(Z)V

   88:  return

}

由上述字节码我们可以看出 int a = 1000, b = 1000;System.out.println(a == b);执行的是if_icmpne命令，比较的是2个int值是否相等。在此返回为true。

而 Integer c = 1000, d = 1000;System.out.println(c==d);执行的是if_acmpne命令，比较的是对象引用地址。查看jdk源码

    public static Integer valueOf(int i) {

    final int offset = 128;

    if (i >= -128 && i <= 127) { // must cache

        return IntegerCache.cache[i + offset];

    }

        return new Integer(i);

    }

此时的值为1000，不在-128~127范围内。所以变量c和d是2个不同的对象。因此System.out.println(c==d);返回结果为false。

而 Integer e = 100, f = 100;System.out.println(e == f);  用的是Integer缓存中的同一对象，因此返回结果为true。