java - 我在java代码中发现了变量声明 "UI variableName;"。那是什么意思？

Question

我下载了流行的“Connect 6”游戏的java源代码。在用户界面类中，它在很多情况下使用“UI”，但没有相关的类或导入库。我想知道其中的原因。 (代码链接:http://kevinverhoef.nl/connect6.htm)

package userinterface;

import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;

import javax.swing.Icon;
import javax.swing.ImageIcon;
import javax.swing.JLabel;

import logic.Stone;


/**
* A graphical representation of the board.
* It also handels the mouse clicks on the board for placing human player stones.
*/
public class BoardObject extends JLabel implements MouseListener {
private static final long serialVersionUID = 1L;

UI applet;

/**
 * Constructor
 */
public BoardObject(UI applet) {
    Icon c = new ImageIcon(getClass().getResource("field.GIF"));
    this.setIcon(c);
    this.setBounds(0, 0, 650, 672);
    this.addMouseListener(this);
    this.applet = applet;
}

/**
 * Handles the mouse clicks for placing stone.
 */
public void mouseClicked(MouseEvent e) {
    // Offset from the board image.
    int topOffset = 16;
    int leftOffset = 26;

    // determine positions on the field
    int x = (int) Math.floor((e.getX() - leftOffset) / 32);
    int y = (int) Math.floor((e.getY() - topOffset) / 32);

    if (x < 19 && y < 19) {

        // Voeg toe aan bord
        Stone newStone = new Stone(x, y, applet.controller.playingColor);

        // Probeer te plaatsen
        if (newStone.place(applet.board)) {
            newStone.stoneNr = applet.controller.getNextStoneNr();
            applet.drawStones();

            applet.controller.addStone(newStone);

            if (applet.inputEnabled) {
                // Check to see next step
                if (applet.controller.firstStone) {
                    applet.step();
                }
            }

        }
    }
}

public void mouseEntered(MouseEvent arg0) {

}

public void mouseExited(MouseEvent arg0) {

}

public void mousePressed(MouseEvent arg0) {

}

public void mouseReleased(MouseEvent arg0) {

}

}

Answer 1

尽管源代码中不存在 UI.java，但如果您查看 .jar 文件，您会在同一包中找到 UI.class(.jar 文件可以由任何 .zip 归档程序打开)。如果您对 UI.class 内容感兴趣，请使用 javap 工具或最新版本的 Intellij Idea 对其进行反编译。