Java拆装箱深度剖析

public class Main{
  public static void main(String[] args){

    Integer num1 = 100;
    Integer num2 = 100;
    Integer num3 = 200;
    Integer num4 = 200;

    '''//输出结果'''
    System.out.println(num1==num2);
    System.out.println(num3==num4);
  }
}

public static Integer valueOf(int i) {
  assert IntegerCache.high >= 127;
  if (i >= IntegerCache.low && i <= IntegerCache.high)
    return IntegerCache.cache[i + 128];
  return new Integer(i);
  }

'''// IntegerCache，一个内部类，注意它的属性都是定义为static final'''
  private static class IntegerCache {
    static final int high; '''//缓存上界，暂为null'''
    static final Integer cache[]; '''//缓存的整型数组'''

    '''// 块，为什么定义为块'''
    static {
      final int low = -128; '''// 缓存下界，不可变了。只有上界可以改变'''

      '''// high value may be configured by property'''
      '''// h值，可以通过设置jdk的AutoBoxCacheMax参数调整（以下有解释），自动缓存区间设置为[-128,N]。注意区间的下界是固定'''
      int h = 127;

      if (integerCacheHighPropValue != null) {
        '''// Use Long.decode here to avoid invoking methods that'''
        '''// require Integer's autoboxing cache to be initialized'''
        // 通过解码integerCacheHighPropValue，而得到一个候选的上界值'''
        int i = Long.decode(integerCacheHighPropValue).intValue();
        '''// 取较大的作为上界，但又不能大于Integer的边界MAX_VALUE'''
        i = Math.max(i, 127);   
        '''// Maximum array size is Integer.MAX_VALUE'''
        h = Math.min(i, Integer.MAX_VALUE - -low);
      }
      high = h; '''//上界确定'''
      '''// 就可以创建缓存块，注意缓存数组大小'''
      cache = new Integer[(high - low) + 1]; //
      int j = low;
      for(int k = 0; k < cache.length; k++)
        cache[k] = new Integer(j++); '''// -128到high值逐一分配到缓存数组'''
    }

    private IntegerCache() {}
  }

public class Main{
  public static void main(String[] args){

    Double i1 = 100.0;
    Double i2 = 100.0;
    Double i3 = 200.0;
    Double i4 = 200.0;

    System.out.println(i1==i2);
    System.out.println(i3==i4);
  }
}

public static Boolean valueOf(boolean b) {
    return (b ? TRUE : FALSE);
  }

public static final Boolean TRUE = new Boolean(true);

'''/** '''
'''* The <code>Boolean</code> object corresponding to the primitive '''
'''* value <code>false</code>. '''
'''*/'''
public static final Boolean FALSE = new Boolean(false);