자바 에서 Integer 형식 값 동일 판단 방법

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;
 }