Java :: Pzzle

Aha.java

import static java.lang.System.out;
public class Aha {
   public static void main(String ... args) {
      Integer a = 1000, b = 1000;
      out.println(a == b);
      
      Integer c = 100, d = 100;
      out.println(c == d);
   }
}

Integer.java

public static Integer valueOf(int i) {
  assert IntegerCache.high >= 127;
  if (i >= IntegerCache.low && i <= IntegerCache.high)
      return IntegerCache.cache[i + (-IntegerCache.low)];
  return new Integer(i);
}

IntegerCache.java

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;
       ...

     }
  ...
}