How to scroll text output in Java?

Question

Say I have a terminal with 30 lines of height.

And say I have a loop that outputs 100 lines of output

for(int i=0; i<100; i++){
  System.out.println(i);
}

Is there a way I can output the first 30 lines, show text that says "Press enter to continue output...", show the next 30 lines when the user presses enter, etc?

I want to do this in the easiest manner possible. If I can use less somehow, that would be excellent.

Update

This needs to be implemented in the Java source code. The following is not a suitable solution:

java program | less'

Also, I will need to programmatically get the height of whatever terminal it is executed in.

score 2 · Answer 1 · answered Oct 13 '11 at 07:11

2

With less:

java program | less

or

for(int i=0; i<100; i++){
    if( i % 30 == 0) {
       System.out.println("Press enter to continue output...");
       System.in.read();
    }    
    System.out.println(i);   
}

answered Oct 13 '11 at 07:11

Prince John Wesley

62,492
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can you elaborate on how I'd use `tput cols`? I'm sort of a Java noob. – maček Oct 13 '11 at 07:23
1

@macek: Get the height of the screen from `tput` and pass it as parameter to java apps. Read `man tput`. – Prince John Wesley Oct 13 '11 at 07:27

score 2 · Answer 2 · answered Oct 13 '11 at 07:12

2

Within Java:

BufferedReader r = new BufferedReader(new InputStreamReader(System.in));

for(int i=0; i<100; i++){
    if (i % 30 == 0) {
        System.out.println("Press enter to continue output...");
        r.readLine();
    }
    System.out.println(i);
}

answered Oct 13 '11 at 07:12

Zarkonnen

22,200
14
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here `30` is statically coded. How can I dynamically get the height of the terminal? – maček Oct 13 '11 at 07:14

score 1 · Accepted Answer · answered Oct 13 '11 at 07:49

1

Either pass tput cols to your java program as a command line arg or system property (java -DTermHeight=`tput cols`) or fetch it during runtime using Runtime.getRuntime().exec("tput cols")

Store that value in a variable height. Now

   height = (height==0?30:height);
    for(int i=1; i<=100; i++) {
        if (i % height== 0) {
            System.out.println("Press enter to continue output...");
            System.in.read();
        }
        System.out.println(i);
    }

answered Oct 13 '11 at 07:49

Jagat

1,392
2
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Marking this as accepted answer for providing means of getting terminal height using Java. Giving +1 to other answers. – maček Oct 13 '11 at 07:53
I am always getting '80' when running tput cols in Java, even though the same command in my terminal gives me a greater value. I am using JDK 1.7u51 – malaverdiere Apr 16 '14 at 13:49

How to scroll text output in Java?

Update

3 Answers3