.equals（“ 0”）和.equals（'0'）之间的差异

Question

Context:

String comparison using equals with double quotes and single quotes

I tried checking the value of the field "parentId" (String) of one of my business objects as below:

System.out.println("Status 1 = "+myBusObj.getParentId().equals("0"));


System.out.println("Status 2 = "+myBusObj.getParentId().equals('0'));

I get the below output:

Status 1 = true //where parentId was of value 0 (String)

Status 2 = false //where parentId was of value 0 (String)

Problem: Why Status 1 is true but Status 2 is false ?

Answer 1

The difference is that in the first case you are comparing with a one character String , and in the second case you are comparing with a Character object.

Strings and Characters are not comparable using equals(Object) ; hence the false in the second case.

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(There is a slight subtlety here ... in that '0' is a char literal that is being autoboxed to give you the Character object. Prior to Java 5 where autoboxing was added to the language, the .equals('0') call would be a compilation error. This is one of those examples where autoboxing is actually a hinderance ...)

Answer 2

Status 1 : You try to compare string object to string object("String" String object) so result will be true.

Status 2 : You try to compare string object to character object('Character' character object) so that result will be false.

Thanks.

Answer 3

双引号将字符串括起来，单引号将字符括起来。