Comparing A String To Integer, Not Working?

Question

Basically I am developing a program that involves matrices, I am AWARE AND DO NOT CORRECT that the matrix provided can be a simple array but that disproves what I am going for here.

Anyways the code provided below supplies 3 methods that each have a code that I have tried to compare the two values and in each case, it fails. If anyone can point out the error, that would be great.

public class TestingLength {

public static String[][] locatedNum = {{"1","2","3"}}; public static int num = 3; public static void test() { System.out.println("Finding Number " + locatedNum[0][2] + " With Number " + num); if(locatedNum[0][2] == ""+num) { System.out.println("Example Worked!"); return; }else System.out.println("Example Failed!"); } public static void test2() { System.out.println("Finding Number " + locatedNum[0][2] + " With Number " + num); if(locatedNum[0][2].equals(num)) { System.out.println("Example Worked!"); return; }else System.out.println("Example Failed!"); } public static void test3() { String s = Integer.toString(num); System.out.println("Finding Number " + locatedNum[0][2] + " With Number " + num); if(locatedNum[0][2] == s) { System.out.println("Example Worked!"); return; }else System.out.println("Example Failed!"); } public static void main(String[] args) { test(); test2(); test3(); }

}

blueygh2 · Accepted Answer · 2014-03-20 23:42:01Z

Your first example works, if you change

if(locatedNum[0][2] == ""+num) {

to

if(locatedNum[0][2].equals(""+num)) {

Here, you are comparing Strings, and Strings should always be compared using .equals. Otherwise, you are comparing the String pointers, which are most of the time not the same.

Your second test works, if you change

if(locatedNum[0][2].equals(num)) {

to

if(Integer.parseInt(locatedNum[0][2]) == num) {

In this case, you are comparing Integer values, and == is a valid choice. However, you have to convert your String value from locatedNum to an Integer value as well.

Your third test works, if you change

 if(locatedNum[0][2] == s) {

to

 if(locatedNum[0][2].equals(s) {

If you are comparing strings, always use .equals instead of ==.

Thank you it worked, I actually laughed because of how close I was and was surprised to see that you cannot do .equals then an integer but w/e. Thanks again.

Joshua Goldberg · Accepted Answer · 2014-03-20 23:33:44Z

Your first example uses == to compare two Strings that are not the same object. (== says "are you the same object.) It would work fine with .equals.

Your second is stranger, comparing the String directly to the int without the ""+num conversion you used earlier to convert to a String

Your third has the same == problem.

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