String与Long类型比较的陷阱 博客分类： codes

public class LongTest {
	public static void main(String[] args) {
		Long tt = 0l;
		
		System.out.println(tt);
		
		boolean flag = "0".equals(tt);
		boolean flag1 = "0".equals(tt.toString());
		
		System.out.println(flag);
		System.out.println(flag1);
	}
}

输出结果:
0
false
true


boolean flag = "0".equals(tt); 

分析:
在这段代码中tt为Long类型，不同类型对象比较永远返回false

String#equals

public boolean equals(Object anObject) {
        if (this == anObject) {
            return true;
        }
        if (anObject instanceof String) {
            String anotherString = (String) anObject;
            int n = value.length;
            if (n == anotherString.value.length) {
                char v1[] = value;
                char v2[] = anotherString.value;
                int i = 0;
                while (n-- != 0) {
                    if (v1[i] != v2[i])
                            return false;
                    i++;
                }
                return true;
            }
        }
        return false;
    }