S04 享元模式 Integer源码分析-优快云博客

本文深入探讨了Java中Integer类的缓存机制，详细解释了在[-128,127]范围内整数对象如何被缓存，以及valueOf方法在不同数值范围内的表现。通过对比127和128的实例化过程，揭示了Integer对象在内存中的存储特性。

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java.lang.Integer

在 [-128, 127] 之间的整数，都是直接从缓存中取；

public final class Integer extends Number implements Comparable<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() {}
    }

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

}

测试代码

public class Test {

    public static void main(String[] args) {
        Integer a = Integer.valueOf(127);
        Integer b = 127;

        Integer c = Integer.valueOf(128);
        Integer d = 128;

        System.out.println("a == b : " + (a == b));
        System.out.println("c == d : " + (c == d));
    }

}

输出：