17.4

import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.File;
import java.io.FileNotFoundException;
import java.util.Scanner;

import javax.swing.*;

public class Test_17_4 extends JFrame{
    private JLabel jl1 = new JLabel("Filename");
    private JTextField jt1 = new JTextField("d:\\a.txt",10);
    private JButton jb1 = new JButton("View");
    private JPanel jholdPanel = new JPanel();
    private JP jp1 = new JP();
    private String s;

    public Test_17_4(){
        add(jp1);
    }

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Test_17_4 frame = new Test_17_4();
        frame.setTitle("Test_17_4");
        frame.setSize(400,500);
        frame.setLocationRelativeTo(null);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    class JP extends JPanel{
        private JTextArea jt = new JTextArea();
        private File file;
        private Scanner input;

        public JP(){
            //set textarea
            jt.setLineWrap(true);
            jt.setWrapStyleWord(false);
            jt.setEditable(false);

            JScrollPane scro = new JScrollPane(jt);        

            //create jscrollpanel to hole the textarea
            JScrollPane scrollPane = new JScrollPane(jt);            

            jholdPanel.setLayout(new FlowLayout(FlowLayout.LEFT));
            jholdPanel.add(jl1);
            jholdPanel.add(jt1);
            jholdPanel.add(jb1);

            jb1.addActionListener(new ActionListener(){

                @Override
                public void actionPerformed(ActionEvent arg0) {
                    // TODO Auto-generated method stub
                    s = jt1.getText();
                    try {
                        jp1.setText(s);
                    } catch (FileNotFoundException e) {
                        // TODO Auto-generated catch block
                        e.printStackTrace();
                    }
                }

            });

            setLayout(new BorderLayout(5,5));
            add(scrollPane,BorderLayout.CENTER);
            add(jholdPanel,BorderLayout.SOUTH);
        }

        public void setText(String s) throws FileNotFoundException{
            file = new File(s);
            if(file.canRead() && file.exists()) {
                input = new Scanner(file);
                while(input.hasNext()) {
                    jt.append(input.nextLine());
                    jt.append("\n");
                }
            }
            else System.out.println("does not exists!");
            input.close();
        }
    }

}

效果图：