Java中Integer类型值相等判断方法

public static void main(String[] args) {

  Integer a = 127 ;

  Integer b = 127 ;

  Integer c = 128 ;

  Integer d = 128 ;

  Integer e = 129 ;

  Integer f = 129 ;

  System.out.println(a==b); //true

  System.out.println(c==d); //false

  System.out.println(e==f); //false

  System.out.println(a.equals(b)); //true

  System.out.println(c.equals(d)); //true

  System.out.println(e.equals(f)); //true

  }

/**

  * Cache to support the object identity semantics of autoboxing for values between

  * -128 and 127 (inclusive) as required by JLS.

  *

  * The cache is initialized on first usage. The size of the cache

  * may be controlled by the {@code -XX:AutoBoxCacheMax=<size>} option.

  * During VM initialization, java.lang.Integer.IntegerCache.high property

  * may be set and saved in the private system properties in the

  * sun.misc.VM class.

  */

private static class IntegerCache {

  static final int low = - 128 ;

  static final int high;

  static final Integer cache[];

  static {

   // high value may be configured by property

   int h = 127 ;

   String integerCacheHighPropValue =

   sun.misc.VM.getSavedProperty( "java.lang.Integer.IntegerCache.high" );

   if (integerCacheHighPropValue != null ) {

   try {

    int i = parseInt(integerCacheHighPropValue);

    i = Math.max(i, 127 );

    // Maximum array size is Integer.MAX_VALUE

    h = Math.min(i, Integer.MAX_VALUE - (-low) - 1 );

   } catch ( NumberFormatException nfe) {

    // If the property cannot be parsed into an int, ignore it.

   }

   }

   high = h;

   cache = new Integer[(high - low) + 1 ];

   int j = low;

   for ( int k = 0 ; k < cache.length; k++)

   cache[k] = new Integer(j++);

   // range [-128, 127] must be interned (JLS7 5.1.7)

   assert IntegerCache.high >= 127 ;

  }

  private IntegerCache() {}

  }

public boolean equals(Object obj) {

  if (obj instanceof Integer) {

   return value == ((Integer)obj).intValue();

  }

  return false ;

  }