java - 用 Java 创建 Web 浏览器

Question

我想知道是否有人可以帮助我找出我的代码有什么问题。我正在尝试创建一个网络浏览器后退和前进按钮。我使用 Java“Deque”(类似于具有更多功能的堆栈)来跟踪当前和以前访问的页面。问题是经过多次调试后我不知道出了什么问题。由于某种原因，订单没有保留，我不明白为什么。任何帮助表示赞赏。到目前为止，该代码仅适用于超链接，但如果我能让它工作，那么当用户手动输入 URL 时，很容易让其他部分工作。谢谢:)

import javax.swing.*;
import javax.swing.event.HyperlinkEvent;
import javax.swing.event.HyperlinkListener;
import java.awt.*;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.io.IOException;
import java.util.ArrayDeque;
import java.util.Deque;

/**
 * This class includes Jbuttons, JTextFields, ScrollPane and View
 * Created by Nash on 12/16/2015.
 */
public class Controller extends JPanel implements ActionListener, HyperlinkListener {

    private JButton button;
    private JButton back;
    private JButton front;
    private JTextField addressBar;
    private JScrollPane scrollBar;
    private View view;
    private int padding = 5;
    private String current = "https://www.kth.se";
    private Deque<String> historyBack = new ArrayDeque<>();
    private Deque<String> historyFront = new ArrayDeque<>();


    /**
     * Constructor name: Controller
     * Includes:    all the buttons
     *              actionPerformed method
     *              hyperlinkUpdate method
     * @param v
     */
    public Controller(View v){

        this.view = v;

        this.setLayout(new GridBagLayout());
        GridBagConstraints c = new GridBagConstraints();

        /* Back button */
        back = new JButton("<");
        back.setName("back");
        back.setEnabled(false);
        back.addActionListener(this);
        c.fill = GridBagConstraints.HORIZONTAL;
        c.weightx = 0.0;
        c.weighty = 0.0;
        c.gridx = 0;
        c.gridy = 0;
        c.ipady = padding;
        this.add(back, c);

        /* Front button */
        front = new JButton(">");
        front.setName("front");
        front.setEnabled(false);
        front.addActionListener(this);
        c.fill = GridBagConstraints.HORIZONTAL;
        c.weightx = 0.0;
        c.weighty = 0.0;
        c.gridx = 1;
        c.gridy = 0;
        c.ipady = padding;
        this.add(front, c);

        /* URL address bar */
        addressBar = new JTextField();
        addressBar.addActionListener(this);
        c.fill = GridBagConstraints.HORIZONTAL;
        c.weightx = 1.0;
        c.weighty = 0.0;
        c.gridx = 2;
        c.gridy = 0;
        this.add(addressBar, c);

         /* Go button */
        button = new JButton("Go!");
        button.addActionListener(this);
        c.fill = GridBagConstraints.HORIZONTAL;
        c.weightx = 0.0;
        c.weighty = 0.0;
        c.gridx = 3;
        c.gridy = 0;
        c.ipady = padding;
        this.add(button, c);

        this.view.addHyperlinkListener(this);

        scrollBar = new JScrollPane(v);
        c.fill = GridBagConstraints.BOTH;
        c.weightx = 1.0;
        c.weighty = 1;
        c.gridx = 0;
        c.gridy = 1;
        c.gridwidth = 4;
        c.insets = new Insets(10,0,10,0);
        this.add(scrollBar, c);

        try{
            view.setPage(current);
            addressBar.setText(current);
        }catch(IOException e){
            System.out.println("Error: " + e.toString());
        }

    }

    /**
     * Method name:     actionPerformed
     * This method sets the page from the user given URL address
     * @param e
     */

    public void actionPerformed(ActionEvent e){
        if(e.getSource() == back){
            if(!historyBack.isEmpty()) {
                goBack();
            }else{
                back.setEnabled(false);
            }
        } else if(e.getSource() == front){
            if(!historyFront.isEmpty()) {
                goFront();
            }else{
                front.setEnabled(false);
            }
        } else {
            try {
                // I can fix this later after the hyperlinks work! Skip this
                current = addressBar.getText();
                System.out.println("n: " + current);          // Print URL
                view.setPage(current);
                addressBar.setText(current);
                historyBack.addFirst(view.getPage().toString());

            }catch(IOException arg0){
                view.setText("404 error... PAGE NOT FOUND!");

                System.out.println("error " + arg0.toString());
            }
        }
    }


    /**
     * Method name:     hyperlinkUpdate
     * This method sets the page to the clicked hyperlink address
     * @param e
     */
    public void hyperlinkUpdate(HyperlinkEvent e){
        if(e.getEventType() == HyperlinkEvent.EventType.ACTIVATED){
            try {
                current = e.getURL().toExternalForm();
                view.setPage(current);
                addressBar.setText(current);
                System.out.println("back saved & front cleared: " + view.getPage().toString());
                historyBack.addFirst(view.getPage().toString());
                historyFront.clear();
                if(!historyBack.isEmpty()) {
                    back.setEnabled(true);
                }else{
                    back.setEnabled(false);
                }
                if(!historyFront.isEmpty()) {
                    front.setEnabled(true);
                }else{
                    front.setEnabled(false);
                }
            }catch(IOException arg0){
                System.out.println("error " + arg0.toString());
            }
        }
    }

    public void goBack(){
        try{
            if(!historyBack.isEmpty()) {
                String removed = historyBack.removeFirst();
                view.setPage(removed);
                addressBar.setText(removed);
                historyFront.add(view.getPage().toString());
                System.out.println("front saved: " + view.getPage().toString());
                if(!historyBack.isEmpty()) {
                    back.setEnabled(true);
                }else{
                    back.setEnabled(false);
                }
                if(!historyFront.isEmpty()) {
                    front.setEnabled(true);
                }else{
                    front.setEnabled(false);
                }
            }
        } catch(IOException arg0){
            System.out.println("Error: " + arg0.toString());
        }
    }

    public void goFront(){
        try{
            if(!historyFront.isEmpty()) {
                String removed = historyFront.removeFirst();
                view.setPage(removed);
                addressBar.setText(removed);
                historyBack.add(view.getPage().toString());
                System.out.println("back saved: " + view.getPage().toString());
                if(!historyFront.isEmpty()) {
                    front.setEnabled(true);
                }else{
                    front.setEnabled(false);
                }
                if(!historyBack.isEmpty()) {
                    back.setEnabled(true);
                }else{
                    back.setEnabled(false);
                }

            }
        } catch(IOException arg0){
            System.out.println("Error: " + arg0.toString());
        }
    }

}

Answer 1

historyBack 和 historyFront 都应该像堆栈一样工作，如下所示:

• 单击链接时，会将当前页面插入“后”堆栈，清除“前”堆栈，并显示新页面。

• 单击后退按钮时，会将当前页面插入“前”堆栈，从“后”堆栈弹出到顶部值，然后显示该页面。

• 单击前进按钮时，会将当前页面插入“后”堆栈，从“前”堆栈弹出到顶部值，然后显示该页面。

如您所见，这是纯粹的堆栈操作。

Deque具有堆栈方法 push() 和 pop()，实现与 addFirst() 和 removeFirst() 相同>。您可以直接调用它们，但使用 push() 和 pop() 有助于阐明堆栈功能。

或者，您可以调用 addLast() 和 removeLast()，其中 add() 与 同义addLast()。

如果您想要堆栈功能，您不能做的就是混合它们，而您却做到了。

搜索代码以使用 historyBack 显示:

historyBack.isEmpty()
historyBack.addFirst()
historyBack.removeFirst()
historyBack.add()          <==== WRONG

搜索代码以使用 historyFront 显示:

historyFront.isEmpty()
historyFront.clear()
historyFront.add()         <==== WRONG
historyFront.removeFirst()

你正在混合它们!!!改为使用push()和pop()，你就不会意外地混合它们了。