Comparing two strings in android

Question

Possible Duplicate:
Comparing two identical strings with == returns false

I am having real hard time with solving this code. This might look silly but I am not able to figure out what is happening. I am parsing a JSONArray(No big deal!) I am traversing the array with a for loop. I want to break the loop when the user input and the value matches. Here is my code

String regi = null;
JSONObject studentObject = null;
try {
JSONArray returned = test.getInternetData();
int i;
for (i = 0; i < returned.length(); i++) {
    studentObject = returned.getJSONObject(i);
    regi = studentObject.getString("REGISTRATION_NO");
    if (regi == reg) {
        name = studentObject.getString("STUDENT_NAME");
        break;
    }
}
course = studentObject.getString("COURSE_CODE");
Log.d("Details", name + course + regi + i);//Out put: nullGraduate081018394:name - null
//course: Graduate (same for all), regi: last registration number, 
//i: giving totalnumber of objects

As per my knowledge the loop should stop when it finds a match. The COURSE_CODE will be corresponding to the student. Am I missing something?

Please note: The function getInternetData() is returning the whole JSON Array. The loop is completely traversing every object.

I am not sure which line is causing trouble. I think my case is bit different — Dibya Panda, Oct 05 '12 at 19:31
what is name here that you are printing in log? It doesnt have any data (it is a null variable as from the post you did) — G_S, Oct 05 '12 at 19:32
@Sharath I am sure I am not comparing null variables. Which varible is null can you please point out? — Dibya Panda, Oct 05 '12 at 19:34
its not comparing but just try changing this line Log.d("Details", name + course + regi + i) to Log.d("Details", name + " - "+course +" - "+ regi +" - "+ i) and be back with the output you are getting in log — G_S, Oct 05 '12 at 19:36
Doesn't change much. I am getting something like this: `null`-`Graduate`-`081018394`-`18`. Where as I should get my name in place of null, my registration number and my slno. I am getting all details form last object and name turns to be null. — Dibya Panda, Oct 05 '12 at 19:39
and even change if (regi == reg) { name = studentObject.getString("STUDENT_NAME"); break; } to any of the suggested ones below. The one you wrote just compares memory locations as far as i know and not the content — G_S, Oct 05 '12 at 19:39
So sorry server was not responding. After changing the `==` it works. Thanks — Dibya Panda, Oct 05 '12 at 19:43

score 2 · Accepted Answer · answered Oct 05 '12 at 19:24

2

Strings cannot be compared with == in Java. You have to use string1.equals(string2).

answered Oct 05 '12 at 19:24

Perley

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score 1 · Answer 2 · answered Oct 05 '12 at 19:25

1

Use regi.equals(reg) or regi.contentEquals(reg) instead of == and you will be fine :-)

answered Oct 05 '12 at 19:25

slezadav

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score 1 · Answer 3 · answered Oct 05 '12 at 19:25

1

use regi.contentEquals(reg) or !regi.contentEquals(reg) for comparison

answered Oct 05 '12 at 19:25

CQM

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score 1 · Answer 4 · answered Oct 05 '12 at 19:25

1

you should use regi.contentEquals(reg)

answered Oct 05 '12 at 19:25

Apostolos

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String hi = "hi"; String hello = "hi"; if(hi==hello){ //do something } This works. – Dibya Panda Oct 05 '12 at 19:27
And this tends to not: `char c = 'i'; String a = "hi"; String b = "h" + c; if (a == b) { //something }`. `==` does an object comparison, whereas `equals()` does a `String` comparison. Read through the actual answer I linked. – kabuko Oct 05 '12 at 19:36
OK then try the sysout way... System.out.println("regi: -" + regi + "- reg: -" + reg + "-"); and see if you can spot any weird thing :) – Apostolos Oct 05 '12 at 19:43
@DibyaPanda: Java interns String literals. So when you create to String literals `String a = "..."; String b = "..."`, it first adds the String "..." to a table of interned Strings, then when you create the second String b, it looks up "...", sees it in the table of intered Strings, and b will point to the same String a does. However, when you are not literally declaring Strings, this will not always work. == checks to see if two primitives have same value or if two objects point to the same underlying object. – aamit915 Oct 05 '12 at 19:54

G_S · Answer 5 · 2012-10-06T02:54:21.960

0

try using this

JSONArray returned = test.getInternetData();
int i;
for (i = 0; i < returned.length(); i++) {
// added the below line
studentObject = new JsonObject();
studentObject = returned.getJSONObject(i);
regi = studentObject.getString("REGISTRATION_NO");
if (regi.equals(reg)) {
    name = studentObject.getString("STUDENT_NAME");
    break;
}
}

instead of just

JSONArray returned = test.getInternetData();
int i;
for (i = 0; i < returned.length(); i++) {
studentObject = returned.getJSONObject(i);
regi = studentObject.getString("REGISTRATION_NO");
if (regi == reg) {
    name = studentObject.getString("STUDENT_NAME");
    break;
}
}

edited Oct 06 '12 at 02:54

answered Oct 05 '12 at 19:43

G_S

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I think you were right using `==` causes problem. I think the code your code should be updated. – Dibya Panda Oct 05 '12 at 19:46
yes yes sorry for the mistake – G_S Oct 06 '12 at 02:53

Comparing two strings in android

5 Answers5