ParenMatcher.java Source code

Introduction

Here is the source code for ParenMatcher.java

Source

/*
Java Swing, 2nd Edition
By Marc Loy, Robert Eckstein, Dave Wood, James Elliott, Brian Cole
ISBN: 0-596-00408-7
Publisher: O'Reilly 
*/
// ParenMatcher.java
//A simple parenthesis matcher.

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JScrollPane;
import javax.swing.JTextPane;
import javax.swing.text.AttributeSet;
import javax.swing.text.BadLocationException;
import javax.swing.text.SimpleAttributeSet;
import javax.swing.text.StyleConstants;
import javax.swing.text.StyleContext;
import javax.swing.text.StyledDocument;

public class ParenMatcher extends JTextPane implements Runnable {

    public static Color[] matchColor = { Color.blue, Color.magenta, Color.green };

    public static Color badColor = Color.red;

    private AttributeSet[] matchAttrSet;

    private AttributeSet badAttrSet;

    public ParenMatcher() {
        // create an array of AttributeSets from the array of Colors
        StyleContext sc = StyleContext.getDefaultStyleContext();
        badAttrSet = sc.addAttribute(SimpleAttributeSet.EMPTY, StyleConstants.Foreground, badColor);
        matchAttrSet = new AttributeSet[matchColor.length];
        for (int j = 0; j < matchColor.length; j += 1)
            matchAttrSet[j] = sc.addAttribute(SimpleAttributeSet.EMPTY, StyleConstants.Foreground, matchColor[j]);
    }

    // match and color the parens/brackets/braces
    public void run() {
        StyledDocument doc = getStyledDocument();
        String text = "";
        int len = doc.getLength();
        try {
            text = doc.getText(0, len);
        } catch (BadLocationException ble) {
        }
        java.util.Stack stack = new java.util.Stack();
        for (int j = 0; j < text.length(); j += 1) {
            char ch = text.charAt(j);
            if (ch == '(' || ch == '[' || ch == '{') {
                int depth = stack.size();
                stack.push("" + ch + j); // push a String containg the char and
                // the offset
                AttributeSet aset = matchAttrSet[depth % matchAttrSet.length];
                doc.setCharacterAttributes(j, 1, aset, false);
            }
            if (ch == ')' || ch == ']' || ch == '}') {
                String peek = stack.empty() ? "." : (String) stack.peek();
                if (matches(peek.charAt(0), ch)) { // does it match?
                    stack.pop();
                    int depth = stack.size();
                    AttributeSet aset = matchAttrSet[depth % matchAttrSet.length];
                    doc.setCharacterAttributes(j, 1, aset, false);
                } else { // mismatch
                    doc.setCharacterAttributes(j, 1, badAttrSet, false);
                }
            }
        }

        while (!stack.empty()) { // anything left in the stack is a mismatch
            String pop = (String) stack.pop();
            int offset = Integer.parseInt(pop.substring(1));
            doc.setCharacterAttributes(offset, 1, badAttrSet, false);
        }
    }

    // unset the foreground color (if any) whenever the user enters text
    // (if not for this, text entered after a paren would catch the paren's
    // color)
    public void replaceSelection(String content) {
        getInputAttributes().removeAttribute(StyleConstants.Foreground);
        super.replaceSelection(content);
    }

    // return true if 'left' and 'right' are matching parens/brackets/braces
    public static boolean matches(char left, char right) {
        if (left == '(')
            return (right == ')');
        if (left == '[')
            return (right == ']');
        if (left == '{')
            return (right == '}');
        return false;
    }

    public static void main(String[] args) {
        JFrame frame = new JFrame("ParenMatcher");

        final ParenMatcher matcher = new ParenMatcher();
        matcher.setText("int fact(int n) {\n" + "  if (n <= 1) return 1;\n" + "  return(n * fact(n-1));\n" + "}\n");
        frame.getContentPane().add(new JScrollPane(matcher), BorderLayout.CENTER);

        JButton matchButton = new JButton("match parens");
        matchButton.addActionListener(new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                matcher.run();
            }
        });
        frame.getContentPane().add(matchButton, BorderLayout.SOUTH);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setSize(200, 150);
        frame.setVisible(true);
    }
}