为什么 Java 中“1000==1000”为false，而”100==100“为true？

Integer a = 1000, b = 1000;      System.out.println(a == b);//1    Integer c = 100, d = 100;      System.out.println(c == d);//2

falsetrue

Integer c = 100;

Integer i = Integer.valueOf(100);

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

Integer c = 100, d = 100;

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

public static void main(String[] args) throws NoSuchFieldException, IllegalAccessException {
      Class cache = Integer.class.getDeclaredClasses()[0]; //1      Field myCache = cache.getDeclaredField("cache"); //2      myCache.setAccessible(true);//3
      Integer[] newCache = (Integer[]) myCache.get(cache); //4      newCache[132] = newCache[133]; //5
      int a = 2;      int b = a + a;      System.out.printf("%d + %d = %d", a, a, b); //    }