Why does if statement never equal "0" or "1" ? I print variable "line" and it is a "0" or "1". But IF statement never works.

Question

/**
 * @(#)StringToFile.java
 *
 *
 * @author 
 * @version 1.00 2016/2/14
 */
package StringToFile;
import java.io.IOException;
import java.nio.charset.Charset;
import java.nio.file.Files;
import java.nio.file.Paths;
import java.util.List;


public class StringToFile {

public static void main(String[] args) throws IOException {

 read("0");
}

public static String read(String msg2) throws IOException {

This is hard coded read of text file

List<String> lines = Files.readAllLines(Paths.get("g:/dungeontreasure/DMJ-solito-v2.12/test.txt"), Charset.defaultCharset());
for (String line : lines) {

msg2 is assigned what was read from text file. I hope.

msg2 = line; //  I assign msg2 what was read from file.

Now, I print out the contents of the text file. this part works.

System.out.println("line read:" + line); // I print out line

Now I check if the text file had a "1" in it, but this never works.

if (msg2==("1")) {
    System.out.println("check read: " + msg2);  // check to see what we read. But this never works.

        }

Now I check if the text file had a "0" in it, but it never works.

if (msg2==("0")) {
System.out.println("check read: " + msg2); // check to see what we read. 



        }

}  

return(msg2);
}

}

Not really a duplicate because the problem is not on comparing string using equals or == but on the hidden content of the string. — Davide Lorenzo MARINO, Feb 20 '16 at 13:47

score 0 · Accepted Answer · answered Feb 20 '16 at 13:32

0

If you need to compare objects use always the method .equals(), not the operator ==.

Using the operator == test for the same object (same location in memory), instead the method .equals() check for the same content.

So instead of

if (msg2==("1")) {

your code should be

if (msg2.equals("1")) {

answered Feb 20 '16 at 13:32

Davide Lorenzo MARINO

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I tried the if (msg2.equals("1")) but it still doesn't work. There must be something else that is wrong. – captainx Feb 20 '16 at 13:38
Check for the length of your string. Perhaps there are white spaces. – Davide Lorenzo MARINO Feb 20 '16 at 13:39
Yes Davide, you are correct. The text file is being written by another program and it is leaving a few spaces. I don't know why. Is there a way in Java to read only the first character of a text file? – captainx Feb 20 '16 at 13:45
You can read it and use the trim() function to remove spaces at the beginning and at the end of the string. – Davide Lorenzo MARINO Feb 20 '16 at 13:46
I used msg2.trim(), but the IF statements didn't seem to work. I think mabie I need to just read 1 character from text file. That's all I actually need. Not sure what method to use. – captainx Feb 20 '16 at 13:54
Actually trimming or read only one char has the same effect in this situation. – Davide Lorenzo MARINO Feb 20 '16 at 13:55
It works! Thank you David. :) – captainx Feb 20 '16 at 14:05

Why does if statement never equal "0" or "1" ? I print variable "line" and it is a "0" or "1". But IF statement never works.

1 Answers1