关于Integer的"=="_integer == 1-优快云博客

本文深入探讨Java中Integer类的内部实现机制，特别是自动装箱如何将基本类型转换为包装类实例，以及在特定范围内如何通过缓存优化性能。文章详细解释了IntegerCache的作用和原理，帮助开发者理解Java内存管理和性能优化的关键点。

public static void main(String []args) {
		Integer a = 1;
		Integer b = 1;
		Integer c = 200;
		Integer d = 200;
		System.out.println(a == b);
		System.out.println(c == d);
	}

输出结果：

true

false

使用1或者1000赋值给Integer时，Java会翻译为Integer.valueof(xxx),附上源码，在-128到127之间的时候直接return IntegerCache.cahe[]了，因此出现了这个结果

    private static class IntegerCache {
        static final int high;
        static final Integer cache[];

        static {
            final int low = -128;

            // high value may be configured by property
            int h = 127;
            if (integerCacheHighPropValue != null) {
                // Use Long.decode here to avoid invoking methods that
                // require Integer's autoboxing cache to be initialized
                int i = Long.decode(integerCacheHighPropValue).intValue();
                i = Math.max(i, 127);
                // Maximum array size is Integer.MAX_VALUE
                h = Math.min(i, Integer.MAX_VALUE - -low);
            }
            high = h;

            cache = new Integer[(high - low) + 1];
            int j = low;
            for(int k = 0; k < cache.length; k++)
                cache[k] = new Integer(j++);
        }

        private IntegerCache() {}
    }

    /**
     * Returns a <tt>Integer</tt> instance representing the specified
     * <tt>int</tt> value.
     * If a new <tt>Integer</tt> 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.
     *
     * @param  i an <code>int</code> value.
     * @return a <tt>Integer</tt> instance representing <tt>i</tt>.
     * @since  1.5
     */
    public static Integer valueOf(int i) {
        if(i >= -128 && i <= IntegerCache.high)
            return IntegerCache.cache[i + 128];
        else
            return new Integer(i);
    }