下图为String源码
讲上图中 if ( anObject instanceof Object) 改为if ( this instanceof Object && anObject instanceof Object) 后s.equals("asd")也可以避免NullPointerException
以下代码为仿照仿照上图重写的一个方法 :
public boolean equals(String str , Object anObject){
if (str == anObject) {
return true;
}
if ( str instanceof Object && anObject instanceof Object) {
String anotherString = (String)anObject;
int n = str.length();
if (n == anotherString.length()) {
char v1[] = str.toCharArray();
char v2[] = anotherString.toCharArray();
int i = 0;
int j = 0;
while (n-- != 0) {
if (v1[i++] != v2[j++])
return false;
}
return true;
}
}
return false;
}