How to make JTextArea display a maximum number of characters?

Following are the steps of setting the maximum numbers of characters that a JTextArea can take.

1. Create a Document class that extends the PlainDocument class. 
• In the class create a maxSize field. 
• Override the insertString method so that only the maxSize or less number of characters can be inserted into the document. 
• Create a setMaxSize method for setting the value of the maxSize.
2. Create a Text Area class that extends the JTextArea, which uses the Document created in step 1 as its default document. Add a setMaxSize method to the class that calls the Document's setMaxSize mthod to set the max size for the Document.

Here is the sample code.

import javax.swing.JFrame;

import javax.swing.JPanel;

import javax.swing.JTextArea;

import javax.swing.text.AttributeSet;

import javax.swing.text.BadLocationException;

import javax.swing.text.PlainDocument;

public class TextAreaSize {

    

    private class MyDocument extends PlainDocument {

        private int maxSize = 1000000000;

        

        @Override

        public void insertString(int offset, String s, AttributeSet attributeSet)

                throws BadLocationException {

            int length = s.length();

            if (length == 0) {

                return;

            }

            if (offset + length > maxSize) {

                s = s.substring(0, maxSize - offset);

            }

            super.insertString(offset, s, attributeSet);

        }

        

        public void setMaxSize(int size) {

            maxSize = size;

        }

    }

    

    private class MyTextArea extends JTextArea {

        private MyDocument document;

        

        public MyTextArea (MyDocument d){

            super(d);

            document = d;

        }

        

        public void setMaxSize(int s){

            document.setMaxSize(s);

        }

    }

    

    public TextAreaSize() {

        MyTextArea textArea = new MyTextArea(new MyDocument());

        textArea.setMaxSize(30);

        textArea.setRows(2);

        textArea.setColumns(20);

        

        JPanel panel = new JPanel();

        panel.add(textArea);

        

        JFrame frame = new JFrame();

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

        frame.add(panel);

        frame.setSize(500, 300);

        frame.setVisible(true); 

    }

    

    public static void main(String[] args){

        new TextAreaSize();

    }

}

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