int、integer比较。。。。

来源：互联网发布：php 上传工具编辑：程序博客网时间：2024/06/03 22:32

第一次写这个东东。麻蛋。。。。编辑器都还不会用。

今天突然在一个群里面看到这个问题。几个print结果：

public static void main(String[] args) {Integer a = new Integer(1);int c = 1;Integer b = 1;System.out.println(a == c); // trueSystem.out.println(a == b); // falseInteger f1 = 100, f2 = 100, f3 = 150, f4 = 150;System.out.println(f1 == f2); // trueSystem.out.println(f3 == f4); // false}

1. a==c输出结果为true, ,因为Integer和int比都会自动拆箱（jdk1.5以上）

2.a==b输出结果为false，这应该好理解了，和String一样，在内存中的对象不一样，输出结果为false.

3.f1==f2输出结果为true而f3==f4结果为false，在于java在编译代码的时候会把integer i = 1（或者integer i = new integer(1)）翻译成integer i = integer.valueof(1)；所以关键在于valueof()函数，下面是valueof()函数的源代码(jkd 1.8)：

 /**     * Returns an {@code Integer} instance representing the specified     * {@code int} value.  If a new {@code Integer} instance is not     * required, this method should generally be used in preference to     * the constructor {@link #Integer(int)}, as this method is likely     * to yield significantly better space and time performance by     * caching frequently requested values.     *     * This method will always cache values in the range -128 to 127,     * inclusive, and may cache other values outside of this range.     *     * @param  i an {@code int} value.     * @return an {@code Integer} instance representing {@code i}.     * @since  1.5     */    public static Integer valueOf(int i) {        if (i >= IntegerCache.low && i <= IntegerCache.high)            return IntegerCache.cache[i + (-IntegerCache.low)];        return new Integer(i);    }

IntegerCache类：

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() {}    }

看一下源码大家都会明白，对于-128到127之间的数，integer在new时会进行缓存，当integer f1 = 100时，会进行缓存，下次再写integer f2 = 100时会直接从缓存中取，就不会new一个对象出来了，所以f1==f2为true，f3==f4为false.

。。。。。。

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