JComponents 直到鼠标悬停或我最小化窗口才会出现，以及 JTextField 问题

【问题标题】：JComponents don't appear until mouseover or I minimize the window, and JTextField problemsJComponents 直到鼠标悬停或我最小化窗口才会出现，以及 JTextField 问题
【发布时间】：2016-01-19 13:27:32
【问题描述】：

我是一名来自菲律宾的 10 年级学生，现在 IT 是关于带有 GUI 的 Java。只有基本的。我们的项目是制作一个POS系统。我已经做了一个，但是有一些小问题：

  1. JComponents 不会出现，除非我最小化窗口然后重新打开它（然后所有内容都会显示）或者我将鼠标悬停在它们上（一个接一个）

  2. 对于“支付金额”（screen2）文本字段，我使用小键盘输入字符串，它在第一次输入之前首先显示“null”，因为此文本字段设置为显示“0”首先然后接受来自键盘的输入。但是当程序刚刚运行时我第一次输入内容时，它首先显示“null”。可以清除，但可能会非常混乱。

请原谅我是一个业余爱好者，因为我只是一个学生，这只是一个项目。另外，这是我第一次来这里，如果我做了什么奇怪的事情，请见谅！我使用 BlueJ 顺便说一句。拜托，我正在寻求你的帮助。谢谢！

这是我的源代码：

import javax.swing.*;
import java.awt.*;
import java.awt.event.*;

public class BalikBukid extends JFrame{
public static final int WIDTH = 1500;
public static final int HEIGHT = 750;

private JLabel BalikBukidFarmKitchen, PriceToPay, AmountPaid;
private JButton CaesarSalad, FarmSalad, Karekare, BeefTaPao, Adobo, MushroomChicken, KaningAsul, KaningDilaw, IceCreamBasket, TsokolateIsland;
private JButton Starters, Beef, Chicken, Rice, Dessert;
private JButton one, two, three, four, five, six, seven, eight, nine, zero, clear;
private JButton order, endorders;
private JTextField screen1, screen2;

private static int OrderPrice = 0, Cash, caesars = 0, farmsalds = 0, kare = 0, tapao = 0, adobs = 0, mushroom = 0, asul = 0, dilaw = 0, icecream = 0, islands = 0;;
private static String PayingScreen;

private OrderHandler ordhandler = new OrderHandler();
private MoneyHandler monhandler = new MoneyHandler();
private TransactionHandler transhandler = new TransactionHandler();
private TotalOrdersHandler tordhandler = new TotalOrdersHandler();
public BalikBukid(){
    Container pane = getContentPane();
    pane.setLayout(null);
    setTitle("Balik Bukid POS System");        
    setSize(WIDTH, HEIGHT);
    setVisible(true);
    setResizable(false);
    setDefaultCloseOperation(EXIT_ON_CLOSE);
    pane.setBackground(Color.green);

    //Instantiate the labels and buttons
    BalikBukidFarmKitchen = new JLabel("Balik Bukid Farm & Kitchen");
    Starters = new JButton("STARTERS");
    Beef = new JButton("BEEF");
    Chicken = new JButton("CHICKEN");
    Rice = new JButton("RICE");
    Dessert = new JButton("DESSERT");
    PriceToPay  = new JLabel("Price to pay: ");
    AmountPaid = new JLabel("Price paid: ");
    CaesarSalad = new JButton("<html><center><b>Classic Caesar<br>Salad</b><br>Php 160</center></html>");
    FarmSalad = new JButton("<html><center><b>Balik Bukid<br>Farm Salad</b><br>Php 160</center></html>");
    Karekare = new JButton("<html><center><b>Ang Kare-kare</b><br>Php 210</center></html>");
    BeefTaPao = new JButton("<html><center><b>Garlic Beef<br>Ta Pao</b><br>Php 180</center></html>");
    Adobo = new JButton("<html><center><b>Binalot na<br>Adobong Dilaw</b><br>Php 145</center></html>");
    MushroomChicken = new JButton("<html><center><b>Mushroom Chicken</b><br>Php 160</center></html>");
    KaningAsul = new JButton("<html><center><b>Kaning Asul</b><br>Php 35</center></html>");
    KaningDilaw = new JButton("<html><center><b>Kaning Dilaw</b><br>Php 35</center></html>");
    IceCreamBasket = new JButton("<html><center><b>Ice Cream<br>Basket</b><br>Php 110</center></html>");
    TsokolateIsland = new JButton("<html><center><b>Tsokolate Islands</b><br>Php 180<</center></html>");
    one = new JButton("1");
    two = new JButton("2");
    three = new JButton("3");
    four = new JButton("4");
    five = new JButton("5");
    six = new JButton("6");
    seven = new JButton("7");
    eight = new JButton("8");
    nine = new JButton("9");
    zero = new JButton("0");
    order = new JButton("TRANSACT");
    endorders = new JButton("CHECK OUT");
    screen1 = new JTextField();
    screen2 = new JTextField();
    clear = new JButton("CLEAR");

    //Set the bounds of each button and label
    BalikBukidFarmKitchen.setBounds(570, 10, 300, 50);
    CaesarSalad.setBounds(250, 100, 100, 70);
    FarmSalad.setBounds(355, 100, 100, 70);
    Starters.setBounds(90, 100, 150, 70);
    Karekare.setBounds(250, 180, 100, 70);
    BeefTaPao.setBounds(355, 180, 100, 70);
    Beef.setBounds(90, 180, 150, 70);
    Adobo.setBounds(250, 260, 100, 70);
    MushroomChicken.setBounds(355, 260, 100, 70);
    Chicken.setBounds(90, 260, 150, 70);
    KaningAsul.setBounds(250, 340, 100, 70);
    KaningDilaw.setBounds(355, 340, 100, 70);
    Rice.setBounds(90, 340, 150, 70);
    IceCreamBasket.setBounds(250, 420, 100, 70);
    TsokolateIsland.setBounds(355, 420, 100, 70);
    Dessert.setBounds(90, 420, 150, 70);
    one.setBounds(950, 150, 80, 60);
    two.setBounds(1030, 150, 80, 60);
    three.setBounds(1110, 150, 80, 60);
    four.setBounds(950, 210, 80, 60);
    five.setBounds(1030, 210, 80, 60);
    six.setBounds(1110, 210, 80, 60);
    seven.setBounds(950, 270, 80, 60);
    eight.setBounds(1030, 270, 80, 60);
    nine.setBounds(1110, 270, 80, 60);
    zero.setBounds(950, 330, 80, 60);
    clear.setBounds(1030, 330, 160, 60);
    order.setBounds(570, 500, 120, 60);
    endorders.setBounds(720,500, 120, 60);
    screen1.setBounds(600, 150, 200, 45);
    screen2.setBounds(600, 300, 200, 45);
    PriceToPay.setBounds(600, 130, 200, 20);
    AmountPaid.setBounds(600, 280, 200, 20);

    //Formatting
    BalikBukidFarmKitchen.setFont(new Font("Trebuchet MS", Font.BOLD, 20));
    BalikBukidFarmKitchen.setForeground(Color.BLUE);
    PriceToPay.setFont(new Font("Trebuchet MS", Font.ITALIC, 15));
    PriceToPay.setForeground(Color.BLUE);
    AmountPaid.setFont(new Font("Trebuchet MS", Font.ITALIC, 15));
    AmountPaid.setForeground(Color.BLUE);
    Starters.setFont(new Font("Trebuchet MS", Font.BOLD, 20));
    Starters.setForeground(Color.RED);
    Starters.setBackground(Color.WHITE);
    Beef.setFont(new Font("Trebuchet MS", Font.BOLD, 20));
    Beef.setForeground(Color.RED);
    Beef.setBackground(Color.ORANGE);
    Chicken.setFont(new Font("Trebuchet MS", Font.BOLD, 20));
    Chicken.setForeground(Color.RED);
    Chicken.setBackground(Color.PINK);
    Rice.setFont(new Font("Trebuchet MS", Font.BOLD, 20));
    Rice.setForeground(Color.RED);
    Rice.setBackground(Color.YELLOW);
    Dessert.setFont(new Font("Trebuchet MS", Font.BOLD, 20));
    Dessert.setForeground(Color.RED);
    Dessert.setBackground(Color.MAGENTA);
    screen1.setText("0");
    screen2.setText("0");
    screen1.setFont(new Font("Trebuchet MS", Font.BOLD, 19));
    screen2.setFont(new Font("Trebuchet MS", Font.BOLD, 19));
    screen1.setHorizontalAlignment(JTextField.CENTER);
    screen2.setHorizontalAlignment(JTextField.CENTER);
    screen1.setEditable(false);
    screen2.setEditable(false);

    //Add Action Listener
    CaesarSalad.addActionListener(ordhandler);
    FarmSalad.addActionListener(ordhandler);
    Karekare.addActionListener(ordhandler);
    BeefTaPao.addActionListener(ordhandler);
    Adobo.addActionListener(ordhandler);
    MushroomChicken.addActionListener(ordhandler);
    KaningAsul.addActionListener(ordhandler);
    KaningDilaw.addActionListener(ordhandler);
    IceCreamBasket.addActionListener(ordhandler);
    TsokolateIsland.addActionListener(ordhandler);
    one.addActionListener(monhandler);
    two.addActionListener(monhandler);
    three.addActionListener(monhandler);
    four.addActionListener(monhandler);
    five.addActionListener(monhandler);
    six.addActionListener(monhandler);
    seven.addActionListener(monhandler);
    eight.addActionListener(monhandler);
    nine.addActionListener(monhandler);
    zero.addActionListener(monhandler);
    clear.addActionListener(monhandler);
    order.addActionListener(transhandler);
    endorders.addActionListener(tordhandler);

    //Add to the container
    pane.add(BalikBukidFarmKitchen);
    pane.add(PriceToPay);
    pane.add(AmountPaid);
    pane.add(CaesarSalad);
    pane.add(FarmSalad);
    pane.add(Karekare);
    pane.add(BeefTaPao);
    pane.add(Adobo);
    pane.add(MushroomChicken);
    pane.add(KaningAsul);
    pane.add(KaningDilaw);
    pane.add(IceCreamBasket);
    pane.add(TsokolateIsland);
    pane.add(screen1);
    pane.add(screen2);
    pane.add(one);
    pane.add(two);
    pane.add(three);
    pane.add(four);
    pane.add(five);
    pane.add(six);
    pane.add(seven);
    pane.add(eight);
    pane.add(nine);
    pane.add(zero);
    pane.add(clear);
    pane.add(order);
    pane.add(endorders);
    pane.add(Starters);
    pane.add(Beef);
    pane.add(Chicken);
    pane.add(Rice);
    pane.add(Dessert);
}
public class OrderHandler implements ActionListener{
    public void actionPerformed(ActionEvent e){
        String StringOrderPrice;
        if(e.getActionCommand().equals("<html><center><b>Classic Caesar<br>Salad</b><br>Php 160</center></html>")){
            OrderPrice += 160;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            caesars++;
        }else if(e.getActionCommand().equals("<html><center><b>Balik Bukid<br>Farm Salad</b><br>Php 160</center></html>")){
            OrderPrice += 160;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            farmsalds++;
        }else if(e.getActionCommand().equals("<html><center><b>Ang Kare-kare</b><br>Php 210</center></html>")){
            OrderPrice += 210;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            kare++;
        }else if(e.getActionCommand().equals("<html><center><b>Garlic Beef<br>Ta Pao</b><br>Php 180</center></html>")){
            OrderPrice += 180;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            tapao++;
        }else if(e.getActionCommand().equals("<html><center><b>Binalot na<br>Adobong Dilaw</b><br>Php 145</center></html>")){
            OrderPrice += 145;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            adobs++;
        }else if(e.getActionCommand().equals("<html><center><b>Mushroom Chicken</b><br>Php 160</center></html>")){
            OrderPrice += 160;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            mushroom++;
        }else if(e.getActionCommand().equals("<html><center><b>Kaning Asul</b><br>Php 35</center></html>")){
            OrderPrice += 35;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            asul++;
        }else if(e.getActionCommand().equals("<html><center><b>Kaning Dilaw</b><br>Php 35</center></html>")){
            OrderPrice += 35;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            dilaw++;
        }else if(e.getActionCommand().equals("<html><center><b>Ice Cream<br>Basket</b><br>Php 110</center></html>")){
            OrderPrice += 110;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            icecream++;
        }else if(e.getActionCommand().equals("<html><center><b>Tsokolate Islands</b><br>Php 180<</center></html>")){
            OrderPrice += 180;
            StringOrderPrice = Integer.toString(OrderPrice);
            screen1.setText(StringOrderPrice);
            islands++;
        }
    }
}
public class MoneyHandler implements ActionListener{
    public void actionPerformed(ActionEvent e){
        if(e.getActionCommand().equals("1")){
            PayingScreen += "1";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("2")){
            PayingScreen += "2";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("3")){
            PayingScreen += "3";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("4")){
            PayingScreen += "4";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("5")){
            PayingScreen += "5";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("6")){
            PayingScreen += "6";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("7")){
            PayingScreen += "7";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("8")){
            PayingScreen += "8";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("9")){
            PayingScreen += "9";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("0")){
            PayingScreen += "0";
            screen2.setText(PayingScreen);
        }else if(e.getActionCommand().equals("CLEAR")){
            PayingScreen = "";
            screen2.setText(PayingScreen);
        }  
    }
}
public class TransactionHandler implements ActionListener{
    public void actionPerformed(ActionEvent e){
        int balance, cashinput, IntAmtPaid, change;  
        String Strcashinput;

        IntAmtPaid = Integer.parseInt(PayingScreen);
        if(IntAmtPaid < OrderPrice){
            balance = OrderPrice - IntAmtPaid;
            do{
                Strcashinput = JOptionPane.showInputDialog(null, "Balance: " + balance +"", "Balance", JOptionPane.INFORMATION_MESSAGE);
                cashinput = Integer.parseInt(Strcashinput);
                balance = balance - cashinput;
            }while(balance != 0);
            JOptionPane.showMessageDialog(null, "Balance: 0. Total balance paid. New transaction.", "Total Balance Paid", JOptionPane.INFORMATION_MESSAGE);
            PayingScreen = "";
            OrderPrice = 0;
            screen1.setText("0");
            screen2.setText("0");
        }else if(IntAmtPaid == OrderPrice){
            JOptionPane.showMessageDialog(null, "Balance: 0. Exact amount paid. New transaction.", "Next transaction", JOptionPane.INFORMATION_MESSAGE);
            PayingScreen = "";
            OrderPrice = 0;
            screen1.setText("0");
            screen2.setText("0");
        }else{
            change = IntAmtPaid - OrderPrice;
            JOptionPane.showMessageDialog(null, "Change: " + change + ". New transaction.", "Change", JOptionPane.INFORMATION_MESSAGE);
            PayingScreen = "";
            OrderPrice = 0;
            screen1.setText("0");
            screen2.setText("0");
        }
    }
}
public class TotalOrdersHandler implements ActionListener{
    public void actionPerformed(ActionEvent e){
        JOptionPane.showMessageDialog(null, "TOTAL ORDERS TODAY:\nClassic Caesars Salad: " + caesars + " order/s\nFarm Salad: " + farmsalds + " order/s\nKare-kare: " + kare + " order/s\nBeef Ta Pao: " + tapao + " order/s\nAdobo: " + adobs + " order/s\nMushroom Chicken: " + mushroom + " order/s\nKaning Asul: " + asul + " order/s\nKaning Dilaw: " + dilaw + " order/s\nIce Cream Basket: " + icecream + " order/s\nTsokolate Islands: " + islands + "orders.\nHave a good day!", "Total Orders", JOptionPane.INFORMATION_MESSAGE);
        System.exit(0);
    }
}
public static void main (String[]args){
    BalikBukid body = new BalikBukid();
}
}

另外，我可能会或可能不会局限于我已经在我的程序中导入的包，但如果我们在课堂上讨论它们会更好，这样我可以更了解它们。还有抱歉我用了cmets，哈哈，我用它们是为了不迷路。

【问题讨论】：

    标签： java swing user-interface bluej


    【解决方案1】：

    组件应在框架可见之前添加到框架中。

    所以将以下语句移到构造函数的末尾：

    setVisible(true);

    实际上，为什么不将所有语句移动到构造函数的末尾，以便语句位于一个位置：

    还有：

    1. 变量名称不应以大写字符开头。有些变量名是正确的，有些则不是。保持一致并遵循 Java 约定！！！

    2. 不要使用空布局。 Swing 旨在与布局管理器一起使用。所以摆脱所有的 setBounds(...) 语句并使用适当的布局管理器。

    【讨论】：

    • 谢谢！现在它确实显示了。对不起，我也不太擅长编程，但我会尝试修复变量。关于空问题，我应该如何解决？我应该简单地使用 setSize 和 setLocation 吗？
    【解决方案2】：

    Java GUI 必须在不同的语言环境中使用不同的 PLAF 在不同的操作系统、屏幕尺寸、屏幕分辨率等上工作。因此，它们不利于像素完美布局。而是使用布局管理器，或 combinations of them 以及 white space 的布局填充和边框。

    现在，该建议是解决问题的核心。实现方式如下：

    1. 使用布局（边框和布局内边距）相对于彼此排列组件，并使用布局约束以合乎逻辑的方式调整它们的大小。
    2. （如果将组件放置在面板中）将面板添加到顶级容器。
    3. pack() 顶级容器，用于触发 GUI 的实际验证，并使 TLC 成为显示内容所需的最小尺寸。
    4. （此时调用 frame.setMinimumSize(frame.getSize()); 是一个不错的选择，但可以选择。）
    5. 致电frame.setVisible(true); // show the organized, sized GUI!

    【讨论】：

    • 非常感谢！不过我不明白怎么做..对不起，那些在课堂上没有讨论过，很难理解。
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