GUI add user input to an array

Question

I'm trying to implement a simple program that takes a user input for a certain object in my case called process and i want to store them in an array of processes . I'll take the array size from the user at the start and initialize the array.

The problem is I couldn't figure out a way to take user input, what is the best jcomponent that will take processes up to the size of the array ?

I tried using jTextArea and here my code for reading the input object process is initialised with two number i asked the user to enter each process at a separated line , and split the two numbers with '/'

int size = Integer.parseInt(this.jTextPane1.getText());
processes = new process[size];
for (int i=0; i<processes.length; i++) {
   processes[i] = new process(
      (i+1),
      Integer.parseInt( line[i].substring(0, line[i].indexOf('/'))),
      Integer.parseInt(line[i].substring(line[i].indexOf('/')+1 )));
}

It shows an error for a null pointer Exception, if there is any thing that I could change in my code ? or Do you have a better way ?

Did you debug and check what is null? Did you make sure the user can only enter `number/number` or check whether he did that? — Thomas, May 09 '17 at 12:40
Possible duplicate of [What is a NullPointerException, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-nullpointerexception-and-how-do-i-fix-it) — f1sh, May 09 '17 at 12:42
Split the too complex lines into several elementary ones, use local variables for the results of indexOf and debug step by step or use System.err.println to print the values of local variables Write a unit test dedicated to the parsing of the string with a lot of different inputs, because they may erroneous (user input) — Aubin, May 09 '17 at 12:47

score 0 · Answer 1 · edited May 23 '17 at 12:02

The problem is I couldn't figure out a way to take user input, what is the best jcomponent that will take processes up to the size of the array ?

There isn't anything like best component to receive inputs. Use cases of the components vary from context to context. In your case, you want to receive number value only. You could setup Document filter as described here for this purpose.

https://stackoverflow.com/questions/7632387/jtextarea-only-with-numbers-but-allowing-negative-values

Then you could create button and configure click listener on it and then retrieve the jTextarea value and then process it further according to your requirement.

I have summarized the whole process into this simple code snippet. You can modify it according to your need.

DocumentFilter to stop user entering text and negative integers

import javax.swing.text.*;
import java.util.regex.*;

public class PositiveNumberOnlyFilter extends DocumentFilter
{
    @Override
    public void insertString(DocumentFilter.FilterBypass fb, int offset, String text, AttributeSet attr) throws BadLocationException
    {
        StringBuilder sb = new StringBuilder();
        sb.append(fb.getDocument().getText(0, fb.getDocument().getLength()));
        sb.insert(offset, text);
        if(!containsOnlyNumbers(sb.toString())) return;
        fb.insertString(offset, text, attr);
    }
    @Override
    public void replace(DocumentFilter.FilterBypass fb, int offset, int length, String text, AttributeSet attr) throws BadLocationException
    {
        StringBuilder sb = new StringBuilder();
        sb.append(fb.getDocument().getText(0, fb.getDocument().getLength()));
        sb.replace(offset, offset + length, text);
        if(!containsOnlyNumbers(sb.toString())) return;
        fb.replace(offset, length, text, attr);
    }
    public boolean containsOnlyNumbers(String text)
    {
        Pattern pattern = Pattern.compile("^[1-9]\\d*$");
        Matcher matcher = pattern.matcher(text);
        boolean isMatch = matcher.matches();
        return isMatch;
    }
}

Demo Main Class

import javax.swing.*;
import java.awt.event.*;
import javax.swing.text.AbstractDocument;
import javax.swing.text.DocumentFilter;

public class SimpleNumberOnlyTextAreDemo implements ActionListener {

    JLabel labelOne;
    JTextArea textArea;
    JButton button;

    SimpleNumberOnlyTextAreDemo() {
        JFrame f = new JFrame();
        labelOne = new JLabel();
        labelOne.setBounds(50, 25, 200, 30);
        textArea = new JTextArea();
        textArea.setBounds(50, 75, 200, 25);
        button = new JButton("Click To Create Array");
        button.setBounds(50, 150, 200, 30);
        button.addActionListener(this);
        f.add(labelOne);
        f.add(textArea);
        f.add(button);
        f.setSize(350, 350);
        f.setLayout(null);
        f.setVisible(true);

        DocumentFilter onlyNumberFilter = new AxisJTextFilter();
        ((AbstractDocument) this.textArea.getDocument()).setDocumentFilter(onlyNumberFilter);
    }

    @Override
    public void actionPerformed(ActionEvent e) {
        String text = textArea.getText();
        labelOne.setText("Input is :=  " + text);
    }

    public static void main(String[] args) {
        SimpleNumberOnlyTextAreDemo simpleNumberOnlyTextAreDemo = new SimpleNumberOnlyTextAreDemo();
    }
}

GUI add user input to an array

1 Answers1