The string contain "/" can't be compared in android?

Question

I think Method A will displays "Ok", but in fact it displays "Fails". The Method B can get the correct result "OK".

I'm sure that the function fi.iki.elonen.NanoHTTPD.getMimeTypeForFile("my.css") will return the result "text/css".

I don't understand why the Method A can't get correct result. Is there some bugs with the function fi.iki.elonen.NanoHTTPD.getMimeTypeForFile ?

BTW, Method C can get the correct result "OK".

Method A

String a="text/css";
String b= fi.iki.elonen.NanoHTTPD.getMimeTypeForFile("my.css");

Utility.LogError("B: "+b);

if (a==b){
    Utility.LogError("Ok");
}else{
    Utility.LogError("Fails");
}

Method B

   String a="text/css";
    String b= fi.iki.elonen.NanoHTTPD.getMimeTypeForFile("my.css");

    Utility.LogError("B: "+b);

    if (a.compareTo(b)==0){
        Utility.LogError("Ok");
    }else{
        Utility.LogError("Fails");
    }

Method C

   String a="text/css";
   String b= "text/css";

    Utility.LogError("B: "+b);

    if (a==b){
        Utility.LogError("Ok");
    }else{
        Utility.LogError("Fails");
    }

score 2 · Accepted Answer · edited May 23 '17 at 11:58

2

Method 1

It results to "Fails" It because the actual objects on heap are getting compared when you use == reference : Detailed explanation

Method 2

It results in Ok as a and b contain same text(mime type) in them (using compare to)

Method 3

It results in Ok, as expected.

edited May 23 '17 at 11:58

Community

1
1

answered Jun 02 '16 at 02:45

cafebabe1991

4,928
2
34
42

Thanks! but in fact Method 2 display "OK" – HelloCW Jun 02 '16 at 03:14
Oh yes, actually i did not consider what your method returned.. updated – cafebabe1991 Jun 02 '16 at 03:58

score 1 · Answer 2 · answered Jun 02 '16 at 02:43

1

In method A , you judge "a==b" which means a have the same reference as b.Obviously their reference is different.

answered Jun 02 '16 at 02:43

score 1 · Answer 3 · answered Jun 02 '16 at 02:51

1

Beacause , In the case A, "if(a == b)",a is a memory address ,as the same, b is a memory address ,ofcourse they are not the same ! and In the case B,you compare to a & b 's value! so they are the same .

answered Jun 02 '16 at 02:51

Qikun.Xiong

11
2

score 0 · Answer 4 · answered Jun 02 '16 at 03:30

0

To compare strings in Java you must use equals().

String a = "abc";
String b = "abc";

if(a.equals(b)) {
// true!
}

When you use ==, java is comparing objects references, not its value.

answered Jun 02 '16 at 03:30

Tiago Luz

129
6

The string contain "/" can't be compared in android?

4 Answers4