int和Integer的区别

点击查看示例

public class Test01 {

	public static void main(String[] args) {
		// TODO Auto-generated method stub
		int a=100;
		int b=100;
		int c=200;
		int d=200;
		Integer x=100;
		Integer y=100;
		Integer o=200;
		Integer p=200;
		
		System.out.println(a==b);
		System.out.println(c==d);
		System.out.println(x==y);
		System.out.println(o==p);
		System.out.println(a==x);
		System.out.println(c==o);
	}

}

结果为

true

false

true

原因：

在Integer的底层源码里

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() {}
    }