Detect the ENTER key being pressed

[aaronfsimons]

Hi all I've wriiten a program that asks for various user inputs.

I want to this process to be repeated until the user presses the ENTER key in a certain field

System.out.println("========== Please select a course to modify ==========");
System.out.println("** If course code is not above enter new course code **");
System.out.println("** Press ENTER to QUIT **");
updateCourse = input.next();
if(//user presses enter)){
System.out.println("Finished");

}else{
for(int j = 0; j < testStudent.getAllCourses().size(); j++){
if(updateCourse.equals(testStudent.getCourses(j))) {
System.out.println("Please enter an updated mark for this course");
newMark = input.nextInt();
testStudent.updateMark(updateCourse, newMark);
allStudents.add(testStudent);

}
}
for(int y = 0; y < allStudents.size(); y++){
System.out.print(allStudents.get(y).prepareFullPri nt());
for(int k = 0; k < allStudents.get(y).getAllResults().size(); k++){
System.out.print(":" + allStudents.get(y).getCourses(k) + "-" + allStudents.get(y).getMark(k));
}
System.out.println();
}
}

Hope someone can help thanks.:confused:

[markw8500]

You want to implement KeyListener...

[Fubarable]

You want to implement KeyListener...

But that would require a GUI program. His is a simple console program.

To the OP: I'm not sure that console will do what you want here. Perhaps you want to create a GUI, but I think not, not at your stage of programming. I think you'll want to use a String such as "quit" for the user to type in when he wants the loop to end.

[Eranga]

Yes, key listeners are not working for console application. Either you have to convert your application into UI or use a simple key-word implementation as Fubarable says.

[Singing Boyo]

O.o it can't be this simple. But it is :p If the users presses enter, the length of the String is 0. See the following code:

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


public class ExitOnEnter {

	public static void main(String[]args){
		BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
		while(true){
			System.out.println("Press enter to exit");
			String s = null;
			try {
				s = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			if(s.length() == 0){
				System.out.println("Exiting...");
				System.exit(0);
			}
		}
	}
}

This just runs until the String returned has a length of 0, which means enter was pressed :)

[aaronfsimons]

Thank you singing boyo; it just took some lateral thinking

Legend.

[Eranga]

Actually quite tricky that code. ;) Just read the NULL string from the console. If you have a space character this wont work. My suggestion is use of the exiting code, like type the command exit.

[RamyaSivakanth]

Hi ,
As per Erangas suggestion ,I did small alteration on Singing Boyo code in the if part.Please go thru.


import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class ExitOnEnter {

	public static void main(String[]args){
		BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
		while(true){
			System.out.println("Press enter to exit");
			String s = null;
			try {
				s = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			if((s == null)||
				(s.length() == 0)
					||(s.trim().equals(""))){
				System.out.println("Exiting...");
				System.exit(0);
			}
		}
	}
}

[Eranga]

Seems it's fine actually. But the checking of the length is not necessary, since you trim the string before validation for empty string.

			if(s == null){
				System.out.println("Exiting...");
				System.exit(0);
			}

[Singing Boyo]

The console string won't ever be null though... it will be empty when enter is pressed, but not null. Therefore, checking only for null will not do anything(believe me, I tried it). If you also want to exit if there is a space, use if(s.trim().length() == 0) instead of if(s.length() == 0), but don't use null, it just won't work :p

[Singing Boyo]

Another option to allow it to exit with unlimited spaces...

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;


public class ExitOnEnter {
	
	public static void main(String[]args){
		BufferedReader br= new BufferedReader(new InputStreamReader(System.in));
		while(true){
			System.out.println("Press enter to exit");
			String s = null;
			try {
				s = br.readLine();
			} catch (IOException e) {
				e.printStackTrace();
			}
			if(s.length() == 0 || isStringOfSpaces(s)){
				System.out.println("Exiting...");
				System.exit(0);
			}
		}
	}
	private static boolean isStringOfSpaces(String s){
		for(char c : s.toCharArray()){
			if(c != ' ')
				return false;
		}
		return true;
	}
}

[DarrylBurke]

> private static boolean isStringOfSpaces(String s){

What's wrong with String#trim()?

db

[Singing Boyo]

Haha lol... trim() has never worked well for me, so I always end up making my own methods for it. Should have realized it would work here. trim() doesn't cut white spaces if they are only on one side, as far as I can tell. Maybe it was just some error in my other programs that I fixed later and didn't realize lol.