layout: post
title: "Java中的equals和=="
category: Reading Notes
tags: ["读文章", “Java”]
{% include JB/setup %}
equals和==
StringBuilder s1 = new StringBuilder();
StringBuilder s2 = new StringBuilder();
String s = "abc";
s1.append(s);
s2.append(s);
System.out.println("s1.equals(s2):\t\t" + (s1.equals(s2)));
System.out.println("s1 == s2:\t\t" + (s1 == s2));
String s3 = s + "1";
String s4 = s + "1";
System.out.println("s3 == s4:\t\t" + (s3 == s4));
System.out.println("s3.equals(s4):\t\t" + (s3.equals(s4)));
Object obj1 = new Object();
Object obj2 = new Object();
System.out.println("obj1.equals(obj2):\t" + (obj1.equals(obj2)));
System.out.println("obj1 == obj2:\t\t" + (obj1 == obj2));
执行结果如下
s1.equals(s2): false
s1 == s2: false
s3 == s4: false
s3.equals(s4): true
obj1.equals(obj2): false
obj1 == obj2: false
Object类的equals方法的实现：
public boolean equals(Object obj) {
return (this == obj);
}
Object中的equals就是用==来比较当前对象和传入的参数的。
String的equals实现：
public boolean equals(Object anObject) {
if (this == anObject) {
return true;
}
if (anObject instanceof String) {
String anotherString = (String)anObject;
int n = count;
if (n == anotherString.count) {
char v1[] = value;
char v2[] = anotherString.value;
int i = offset;
int j = anotherString.offset;
while (n-- != 0) {
if (v1[i++] != v2[j++])
return false;
}
return true;
}
}
return false;
}
它去比较内容了。
StringBuilder，在其源码里没有发现equals方法，那么它就继承了Object的实现，用==来比较传进来的参数。