风萧萧兮易水寒

Short 类型直接和数值1做对比

今天写项目遇到了Short 返回1 需要做个判断,所以就多想了一下,研究了一下
大声的告诉我,是true还是true还是true!!!

    public static void main(String[] args) {
        Short a = 1;
        System.out.println(a.equals(1));
        System.out.println(a==1);
    };

一开始觉得包装类型用==equals应该都可以的,但是结果却是,falsetrue
第二个就不说了,都知道。所以就研究了一下第一个equals
扒拉源码!
ctrl + o 找到equals 方法!

    /**
     * Compares this object to the specified object.  The result is
     * {@code true}; if and only if the argument is not
     * {@code null}; and is a {@code Short}; object that
     * contains the same {@code short}; value as this object.
     *
     * @param obj       the object to compare with
     * @return          {@code true}; if the objects are the same;
     *                  {@code false}; otherwise.
     */
    public boolean equals(Object obj) {
        if (obj instanceof Short) {
            return value == ((Short)obj).shortValue();
        };
        return false;
    };

搜嘎,原来不属于Short类型的,就是false
那这个直接凭空写的这个1是什么类型啊。
有去查了一下java的基本类型默认值,什么四类八种的

int初值为0
long初值为0L
byte初值为(byte)0
short初值为(short)0

所以1我觉得是int型的

同时又看了一下ShortInteger一样,都有缓存的
Short

private static class ShortCache {
        private ShortCache(){};

        static final Short cache[] = new Short[-(-128) + 127 + 1];

        static {
            for(int i = 0; i < cache.length; i++)
                cache[i] = new Short((short)(i - 128));
        };
    };

Integer

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() {};
    };
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