Why the if statement from the java code is jumped even if the "module" and "sModule" are equal

Question

I try to select only the files with same module to be displayed on the list view from an sql table. If I'm using if (module == smodule) the app is ok but the if statement is jumped, using if (module.equals(smodule)) the app is crasing.

Thanks @Nambari problem is that I had a null for the value of module in the database.

Thanks @Buhake Sindi for the suggestion 'Instantiate it like String module = ""'

Java code.................:

private void getFiles() {                               //getting data from the SQL database
    String[] columns = {"id", "file", "module", "date", "note"};
    database = helper.getWritableDatabase();
    Cursor cursor = database.query("files", columns, null, null, null, null, null);
    cursor.moveToFirst();
    files.clear();
    while (!cursor.isAfterLast()) {
        String module = cursor.getString(2);
        String smodule = "Alllllll";
        Log.v("test", smodule+" "+module+" <-if m=sm getting sql data /not if");
        if (module.equals(smodule)){
             String file = cursor.getString(1);
             files.add(file);
             Log.v("test", file+" "+files+" <-if m=sm getting sql data/if");
        }
    cursor.moveToNext();
    }
    cursor.close();
    helper.close();

Logcat:

Alllllll null <-if m=sm getting sql data not/if
Alllllll null <-if m=sm getting sql data not/if
Alllllll null <-if m=sm getting sql data not/if
Alllllll null <-if m=sm getting sql data not/if
Alllllll Alllllll <-if m=sm getting sql data not/if
Alllllll Alllllll <-if m=sm getting sql data not/if
Alllllll Alllllll <-if m=sm getting sql data not/if

Error log after replacing == with .equals():

03-28 14:31:03.985: E/SpannableStringBuilder(25898): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
03-28 14:31:03.985: E/SpannableStringBuilder(25898): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
03-28 14:31:15.030: D/AbsListView(25898): Get MotionRecognitionManager
03-28 14:31:15.085: W/ResourceType(25898): Failure getting entry for 0x010802c1 (t=7 e=705) in package 0 (error -75)
03-28 14:31:15.090: W/ResourceType(25898): Failure getting entry for 0x010802c1 (t=7 e=705) in package 0 (error -75)
03-28 14:31:15.225: E/SpannableStringBuilder(25898): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
03-28 14:31:15.225: E/SpannableStringBuilder(25898): SPAN_EXCLUSIVE_EXCLUSIVE spans cannot have a zero length
03-28 14:31:28.950: D/AbsListView(26523): Get MotionRecognitionManager
03-28 14:31:29.060: D/libEGL(26523): loaded /system/lib/egl/libEGL_mali.so
03-28 14:31:29.075: D/libEGL(26523): loaded /system/lib/egl/libGLESv1_CM_mali.so
03-28 14:31:29.080: D/libEGL(26523): loaded /system/lib/egl/libGLESv2_mali.so
03-28 14:31:29.090: D/(26523): Device driver API match
03-28 14:31:29.090: D/(26523): Device driver API version: 10
03-28 14:31:29.090: D/(26523): User space API version: 10 
03-28 14:31:29.090: D/(26523): mali: REVISION=Linux-r2p4-02rel0 BUILD_DATE=Thu Oct 25 08:43:05 KST 2012 
03-28 14:31:29.115: D/OpenGLRenderer(26523): Enabling debug mode 0
03-28 14:31:29.135: W/ResourceType(26523): Failure getting entry for 0x010802c1 (t=7 e=705) in package 0 (error -75)
03-28 14:31:29.145: W/ResourceType(26523): Failure getting entry for 0x010802c1 (t=7 e=705) in package 0 (error -75)
03-28 14:31:30.780: D/AbsListView(26523): Get MotionRecognitionManager
03-28 14:31:30.800: V/test(26523): Alllllll null <-if m=sm getting sql data /not if
03-28 14:31:30.805: D/AndroidRuntime(26523): Shutting down VM
03-28 14:31:30.805: W/dalvikvm(26523): threadid=1: thread exiting with uncaught exception (group=0x4189f2a0)
03-28 14:31:30.810: E/AndroidRuntime(26523): FATAL EXCEPTION: main
03-28 14:31:30.810: E/AndroidRuntime(26523): java.lang.RuntimeException: Unable to start activity ComponentInfo{com.example.cn/com.example.cn.ListView2}: java.lang.NullPointerException
03-28 14:31:30.810: E/AndroidRuntime(26523):    at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2110)
03-28 14:31:30.810: E/AndroidRuntime(26523):    at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2135)
03-28 14:31:30.810: E/AndroidRuntime(26523):    at android.app.ActivityThread.access$700(ActivityThread.java:140)

end

score 4 · Accepted Answer · answered Mar 28 '13 at 14:10

4

if (module == smodule){

should be

  if (module.equals(smodule)){

While comparing String/Objects. It is better to use equals() than ==

== checks for reference equality. equals() checks for object equality.

answered Mar 28 '13 at 14:10

kosa

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It's not only *better*, it's the only (correct) way to compare equality (and not only for Strings) – a_horse_with_no_name Mar 28 '13 at 14:12
@a_horse_with_no_name: agree. But reason why I have better there is, when you compare String literals, == also works. – kosa Mar 28 '13 at 14:14
if I'm using `if (module.equals(smodule)){` is crashing the app – Alexander Mar 28 '13 at 14:24
@MV: Without error message, can't predict what is going on. Update question with error stack. – kosa Mar 28 '13 at 14:26
`==` is **not** guaranteed to work with String literals. You should avoid using that. – a_horse_with_no_name Mar 28 '13 at 14:33
`03-28 14:31:30.800: V/test(26523): Alllllll null – Alexander Mar 28 '13 at 14:37
@MV: It seems NullPointerException. Please edit question and update full stack trace over there. Make sure "module" is not null. – kosa Mar 28 '13 at 14:41

Buhake Sindi · Answer 2 · 2013-03-28T15:45:17.097

2

That's because you are not evaluating the value of the String, instead you are comparing its object reference.

For String value comparison, use the equals() method, like so:

if (module.equals(smodule)) {

Seeing that smodule is never null and that module can be null, to avoid NullPointerException rather do:

if (smodule.equals(module)) {

edited Mar 28 '13 at 15:45

answered Mar 28 '13 at 14:11

Buhake Sindi

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if I'm using `if (module.equals(smodule)){` is crashing the app. – Alexander Mar 28 '13 at 14:27
then make sure that `module` is **never** null. Instantiate it like `String module = "";` – Buhake Sindi Mar 28 '13 at 15:01

score 1 · Answer 3 · answered Mar 28 '13 at 14:13

use module.equals(smodule),

== vs .equals

== -> is a reference comparison ie both objects point to the same memory location
equals() -> evaluates to the comparison of values in the objects
it's .equals(...) though (first letter is not capitalized).
equals will only compare what it is written to compare, no more, no less.
if equals is not overridden, it defaults to ==; that is, it returns true if both variables refer to the same object.
Always remember to override hashCode if you override equals so as not to "break the contract".

score 0 · Answer 4 · edited May 23 '17 at 12:28

0

Please use the .equals method and not == in Java. Tons of discussion already here.

edited May 23 '17 at 12:28

Community

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answered Mar 28 '13 at 14:12

karmanaut

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sorry for the typo. Edited. – karmanaut Mar 28 '13 at 14:13

score 0 · Answer 5 · edited Mar 28 '13 at 14:18

0

if (module == smodule)

should be

if (module.equals(smodule))

== compares object references.

equals() compares object contents.

edited Mar 28 '13 at 14:18

kosa

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answered Mar 28 '13 at 14:12

Achintya Jha

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Why the if statement from the java code is jumped even if the "module" and "sModule" are equal

5 Answers5