Can't set directory path in a JTextField

Question

I've tried to set some directory paths in a JTextField, but nothing displayed in that the JTextField. However, i can print the directory paths one at a time to the console. The following is the code and will explain what I am trying to do:
fileDialog.showOpenDialog(this);
File[] classpath = fileDialog.getSelectedFiles();
if(classpath.length == 0)
return;
String cp = "";
for(int i = 0; i<classpath.length; i++){
//System.out.println(classpath.getPath());
cp.concat(classpath[i].getAbsolutePath());
System.out.println(cp);
jTextField_cp.setText(cp);
if I uncomment the first print statement,each path will be shown on a new line in the console. But when I want to print the pathes of the directories in one time( concatenate them first), there's no output at all (the second print statement), I only got some empty new lines in the console. Is it any problems with the use of "cp.concat()" method?

Answer 1

I'm pretty sure that it'll work if you replace your concat line with this.
cp = cp.concat(classpath.getAbsolutePath());Java strings are passed by the value of their references, so you are only manipulating the value of the reference, the the string itself, unlike other objects. To work around that, assign cp the new string returned from the concat method.