个人笔记(一)正确使用equals方法
程序员文章站
2022-11-30 15:51:13
public static void main(String[] args) {String str = null;if (str.equals("今天星期六")){//Exception in thread "main" java.lang.NullPointerExceptionSystem.out.println(true);}else {System.out.println(false);}}public static void main(String[...
使用equals方法的三种情况:
第一种:
public static void main(String[] args) {
String str = null;
if (str.equals("今天星期六")){//Exception in thread "main" java.lang.NullPointerException
System.out.println(true);
}else {
System.out.println(false);
}
}
第二种:
public static void main(String[] args) {
String str = null;
if (("今天星期六".equals(str))){
System.out.println(true);
}else {
System.out.println(false);//false
}
}
第三种:(推荐使用)
public static void main(String[] args) {
// String str = null;
if ((Objects.equals(null,"今天星期六"))){//java.util.Objects#equals(JDK7 引入的工具类)
System.out.println(true);
}else {
System.out.println(false);//false
}
}
源码分析:
/**
* Returns {@code true} if the arguments are equal to each other
* and {@code false} otherwise.
* Consequently, if both arguments are {@code null}, {@code true}
* is returned and if exactly one argument is {@code null}, {@code
* false} is returned. Otherwise, equality is determined by using
* the {@link Object#equals equals} method of the first
* argument.
*
* @param a an object
* @param b an object to be compared with {@code a} for equality
* @return {@code true} if the arguments are equal to each other
* and {@code false} otherwise
* @see Object#equals(Object)
*/
public static boolean equals(Object a, Object b) {//源码
return (a == b) || (a != null && a.equals(b));
}
本文地址:https://blog.csdn.net/qq_38258824/article/details/107289959
上一篇: java aspose的集成