奇怪的Java题：为什么1000 == 1000返回为False，而100 == 100会返回为True?

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Integer a = 1000, b = 1000; 

System.out.println(a == b);//1

Integer c = 100, d = 100; 

System.out.println(c == d);//2

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false

true

Integer c = 100;

Integer i = Integer.valueOf(100);

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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);

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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); //

    }