java判断两个对象是否相同个方法源码分析

1，错误用法

a.equals(b)  //a 是null, 抛出NullPointException异常

　　

2，正确用法

Objects.equals(a, b)   //这种方法对null值进行了条件判断

　　分析源码

public final class Objects {  
    private Objects() {  
        throw new AssertionError("No java.util.Objects instances for you!");  
    }  
   
    public static boolean equals(Object a, Object b) {  
        return (a == b) || (a != null && a.equals(b));  //null值先通过地址判断
    }  

　　

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;
    }