java 比较与等于！比较字符串或对象？
声明：本页面是StackOverFlow热门问题的中英对照翻译，遵循CC BY-SA 4.0协议，如果您需要使用它，必须同样遵循CC BY-SA许可，注明原文地址和作者信息，同时你必须将它归于原作者（不是我）：StackOverFlow
原文地址: http://stackoverflow.com/questions/10774559/
Warning: these are provided under cc-by-sa 4.0 license. You are free to use/share it, But you must attribute it to the original authors (not me):
StackOverFlow
CompareTo versus Equals! compares strings or objects?
提问by Navy Seal
Fast question
快问
I am comparing a String, should I use equals or compareTo? because I though equals distinguish 2 objects of type String and not just their value...
我正在比较一个字符串，我应该使用 equals 还是 compareTo？因为我虽然等于区分 2 个字符串类型的对象，而不仅仅是它们的值......
which may cause problems since:
这可能会导致问题，因为：
String a = new String("lol");
String b = new String("lol");
are two different objects even if they have the same value?
即使它们具有相同的值，它们是两个不同的对象吗？
Whats exactly difference between equals and compareTo implementations in terms of performance and precision?
就性能和精度而言，equals 和 compareTo 实现之间的确切区别是什么？
回答by Jeffrey
Did you try it?
你试了吗？
String a = new String("foo");
String b = new String("foo");
System.out.println(a == b); // false
System.out.println(a.equals(b)); // true
System.out.println(a.compareTo(b)); // 0
回答by Mesop
First of all ==compares the references to see if the two objects are the same (so ==is on the object).
首先==比较引用以查看两个对象是否相同（对象上也是如此==）。
Then String.equals()verify the equality of the content of two strings while String.compareTo()seek the difference of the content of two strings.
然后String.equals()在String.compareTo()求两个字符串内容的差异的同时，验证两个字符串内容的相等性。
So the two following tests are equivalent:
所以下面的两个测试是等价的：
String str = "my string";
if ( str.equals("my second string")) {/*...*/}
if ( str.compareTo("my second string")==0) {/*...*/}
But, since String.equalsis making a reference check first, it's safe when used against null, while String.compareTowill throws a NullPointerException:
但是，由于String.equals首先进行引用检查，因此在使用时是安全的null，而String.compareTo将抛出一个NullPointerException：
String str = "my string";
if ( str.equals(null)) {/* false */}
if ( str.compareTo(null) {/* NullPointerException */}
回答by Pramod Kumar
String a = new String("lol");
String b = new String("lol");
System.out.println(a == b); // false. It checks references of both sides operands and we have created objects using new operator so references would not be same and result would be false.
System.out.println(a.equals(b)); // true checks Values and values are same
System.out.println(a.compareTo(b)); // checks for less than, greater than or equals. Mainly used in sortings.
