JButtons不会出现JPanel.setLayout（null）;

Question

大家好我正在制作计算器，所以很多按钮必须显示在面板上。 我想找到绝对按钮，所以我称之为'panel.setLayout（null）'但按钮 不会出现所以我发表这个声明，然后我无法处理按钮位置 表达，我该怎么办？ 3个按钮位置的底部是错误的。

class CalcTest extends JFrame implements ActionListener {

private JPanel panel;
static JTextField ansField;
static JButton mcButton, mrButton, msButton, mpButton, mmButton;
static JButton backButton,ceButton,cButton,plusMinusButton,divButton,multiButton,subButton,addButton,rootButton,percentButton,reciprocButton,equalButton,decimalButton;
static JButton oneButton,twoButton,threeButton,fourButton,fiveButton,sixButton,sevenButton,eightButton,nineButton,zeroButton;
static int addClick = 0, subClick = 0, multiClick = 0, divClick = 0, percentClick = 0, reciprocClick = 0;
static double num1, num2, ans;

public CalcTest(){

    // frame basic options

    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    setTitle("Calculator");
    setSize(220,310);
    setResizable(false);
    setLocationRelativeTo(null); 

    panel = new JPanel();
    panel.setSize(220,310);
    **panel.setLayout(null);**

    // adding buttons and stuff

    ansField = new JTextField();
    ansField.setPreferredSize(new Dimension(190,50));
    ansField.setLocation(12,31);
    ansField.setEditable(false);
    ansField.setHorizontalAlignment(JTextField.RIGHT);

    mcButton = new JButton("MC");
    mrButton = new JButton("MR");
    msButton = new JButton("MS");
    mpButton = new JButton("M+");
    mmButton = new JButton("M-");
    backButton = new JButton("←");
    ceButton = new JButton("CE");
    cButton = new JButton("C");
    plusMinusButton = new JButton("±");
    rootButton = new JButton("√");
    sevenButton = new JButton("7");
    eightButton = new JButton("8");
    nineButton = new JButton("9");
    divButton = new JButton("/");
    percentButton = new JButton("%");
    fourButton = new JButton("4");
    fiveButton = new JButton("5");
    sixButton = new JButton("6");
    multiButton = new JButton("*");
    reciprocButton = new JButton("1/x");
    oneButton= new JButton("1");
    twoButton = new JButton("2");
    threeButton = new JButton("3");
    subButton = new JButton("-");
    zeroButton = new JButton("0");
    decimalButton = new JButton(".");
    addButton = new JButton("+");
    equalButton = new JButton("=");


    mcButton.setPreferredSize(new Dimension(34,27));
    mrButton.setPreferredSize(new Dimension(34,27));
    msButton.setPreferredSize(new Dimension(34,27));
    mpButton.setPreferredSize(new Dimension(34,27));
    mmButton.setPreferredSize(new Dimension(34,27));
    backButton.setPreferredSize(new Dimension(34,27));
    ceButton.setPreferredSize(new Dimension(34,27));
    cButton.setPreferredSize(new Dimension(34,27));
    plusMinusButton.setPreferredSize(new Dimension(34,27));
    rootButton.setPreferredSize(new Dimension(34,27));
    sevenButton.setPreferredSize(new Dimension(34,27));
    eightButton.setPreferredSize(new Dimension(34,27));
    nineButton.setPreferredSize(new Dimension(34,27));
    divButton.setPreferredSize(new Dimension(34,27));
    percentButton.setPreferredSize(new Dimension(34,27));
    fourButton.setPreferredSize(new Dimension(34,27));
    fiveButton.setPreferredSize(new Dimension(34,27));
    sixButton.setPreferredSize(new Dimension(34,27));
    multiButton.setPreferredSize(new Dimension(34,27));
    reciprocButton.setPreferredSize(new Dimension(34,27));
    oneButton.setPreferredSize(new Dimension(34,27));
    twoButton.setPreferredSize(new Dimension(34,27));
    threeButton.setPreferredSize(new Dimension(34,27));
    subButton.setPreferredSize(new Dimension(34,27));
    zeroButton.setPreferredSize(new Dimension(34,27));
    decimalButton.setPreferredSize(new Dimension(34,27));
    addButton.setPreferredSize(new Dimension(34,27));
    equalButton.setPreferredSize(new Dimension(34,27));


    mcButton.setFont(new Font("Arial",Font.PLAIN,11));
    mrButton.setFont(new Font("Arial",Font.PLAIN,11));
    msButton.setFont(new Font("Arial",Font.PLAIN,11));
    mpButton.setFont(new Font("Arial",Font.PLAIN,11));
    mmButton.setFont(new Font("Arial",Font.PLAIN,11));
    backButton.setFont(new Font("Arial",Font.BOLD,13));
    ceButton.setFont(new Font("Arial",Font.PLAIN,11));
    cButton.setFont(new Font("Arial",Font.PLAIN,11));
    plusMinusButton.setFont(new Font("Arial",Font.PLAIN,11));
    rootButton.setFont(new Font("Arial",Font.PLAIN,11));
    sevenButton.setFont(new Font("Arial",Font.PLAIN,11));
    eightButton.setFont(new Font("Arial",Font.PLAIN,11));
    nineButton.setFont(new Font("Arial",Font.PLAIN,11));
    divButton.setFont(new Font("Arial",Font.PLAIN,11));
    percentButton.setFont(new Font("Arial",Font.PLAIN,11));
    fourButton.setFont(new Font("Arial",Font.PLAIN,11));
    fiveButton.setFont(new Font("Arial",Font.PLAIN,11));
    sixButton.setFont(new Font("Arial",Font.PLAIN,11));
    multiButton.setFont(new Font("Arial",Font.PLAIN,11));
    reciprocButton.setFont(new Font("Arial",Font.PLAIN,11));
    oneButton.setFont(new Font("Arial",Font.PLAIN,11));
    twoButton.setFont(new Font("Arial",Font.PLAIN,11));
    threeButton.setFont(new Font("Arial",Font.PLAIN,11));
    subButton.setFont(new Font("Arial",Font.PLAIN,11));
    zeroButton.setFont(new Font("Arial",Font.PLAIN,11));
    decimalButton.setFont(new Font("Arial",Font.PLAIN,11));
    addButton.setFont(new Font("Arial",Font.PLAIN,11));
    equalButton.setFont(new Font("Arial",Font.BOLD,13));

    mcButton.setMargin(new Insets(0,0,0,0));
    mrButton.setMargin(new Insets(0,0,0,0));
    msButton.setMargin(new Insets(0,0,0,0));
    mpButton.setMargin(new Insets(0,0,0,0));
    mmButton.setMargin(new Insets(0,0,0,0));
    backButton.setMargin(new Insets(0,0,0,0));
    ceButton.setMargin(new Insets(0,0,0,0));
    cButton.setMargin(new Insets(0,0,0,0));
    plusMinusButton.setMargin(new Insets(0,0,0,0));
    rootButton.setMargin(new Insets(0,0,0,0));
    sevenButton.setMargin(new Insets(0,0,0,0));
    eightButton.setMargin(new Insets(0,0,0,0));
    nineButton.setMargin(new Insets(0,0,0,0));
    divButton.setMargin(new Insets(0,0,0,0));
    percentButton.setMargin(new Insets(0,0,0,0));
    fourButton.setMargin(new Insets(0,0,0,0));
    fiveButton.setMargin(new Insets(0,0,0,0));
    sixButton.setMargin(new Insets(0,0,0,0));
    multiButton.setMargin(new Insets(0,0,0,0));
    reciprocButton.setMargin(new Insets(0,0,0,0));
    oneButton.setMargin(new Insets(0,0,0,0));
    twoButton.setMargin(new Insets(0,0,0,0));
    threeButton.setMargin(new Insets(0,0,0,0));
    subButton.setMargin(new Insets(0,0,0,0));
    zeroButton.setMargin(new Insets(0,0,0,0));
    decimalButton.setMargin(new Insets(0,0,0,0));
    addButton.setMargin(new Insets(0,0,0,0));
    equalButton.setMargin(new Insets(0,0,0,0));

    mcButton.setFocusable(false);
    mrButton.setFocusable(false);
    msButton.setFocusable(false);
    mpButton.setFocusable(false);
    mmButton.setFocusable(false);
    backButton.setFocusable(false);
    ceButton.setFocusable(false);
    cButton.setFocusable(false);
    plusMinusButton.setFocusable(false);
    rootButton.setFocusable(false);
    sevenButton.setFocusable(false);
    eightButton.setFocusable(false);
    nineButton.setFocusable(false);
    divButton.setFocusable(false);
    percentButton.setFocusable(false);
    fourButton.setFocusable(false);
    fiveButton.setFocusable(false);
    sixButton.setFocusable(false);
    multiButton.setFocusable(false);
    reciprocButton.setFocusable(false);
    oneButton.setFocusable(false);
    twoButton.setFocusable(false);
    threeButton.setFocusable(false);
    subButton.setFocusable(false);
    zeroButton.setFocusable(false);
    decimalButton.setFocusable(false);
    addButton.setFocusable(false);
    equalButton.setFocusable(false);

    mcButton.setLocation(12,67);
    mrButton.setLocation(51,67);
    msButton.setLocation(90,67);
    mpButton.setLocation(129,67);
    mmButton.setLocation(168,67);
    backButton.setLocation(12,118);
    ceButton.setLocation(51,118);
    cButton.setLocation(90,118);
    plusMinusButton.setLocation(129,118);
    rootButton.setLocation(168,118);
    sevenButton.setLocation(12,169);
    eightButton.setLocation(51,169);
    nineButton.setLocation(90,169);
    divButton.setLocation(129,169);
    percentButton.setLocation(168,169);
    fourButton.setLocation(12,220);
    fiveButton.setLocation(51,220);
    sixButton.setLocation(90,220);
    multiButton.setLocation(129,220);
    reciprocButton.setLocation(168,220);
    oneButton.setLocation(12,271);
    twoButton.setLocation(51,271);
    threeButton.setLocation(90,271);
    subButton.setLocation(129,271);
    equalButton.setLocation(168,271);
    zeroButton.setLocation(12,322);
    decimalButton.setLocation(90,322);
    addButton.setLocation(129,322);

    panel.add(ansField);

    panel.add(mcButton);
    panel.add(mrButton);
    panel.add(msButton);
    panel.add(mpButton);
    panel.add(mmButton);
    panel.add(backButton);
    panel.add(ceButton);
    panel.add(cButton);
    panel.add(plusMinusButton);
    panel.add(rootButton);
    panel.add(sevenButton);
    panel.add(eightButton);
    panel.add(nineButton);
    panel.add(divButton);
    panel.add(percentButton);
    panel.add(fourButton);
    panel.add(fiveButton);
    panel.add(sixButton);
    panel.add(multiButton);
    panel.add(reciprocButton);
    panel.add(oneButton);
    panel.add(twoButton);
    panel.add(threeButton);
    panel.add(subButton);
    panel.add(equalButton);
    panel.add(zeroButton);
    panel.add(decimalButton);
    panel.add(addButton);

    add(panel);

    // button listener 

    // setvisible

    setVisible(true);
}

public void actionPerformed(ActionEvent e){

}
}





public class Calc {
    public static void main(String args[]){
        CalcTest c = new CalcTest();
    }
}   

Answer 1

在没有LayoutManager的情况下工作时，您需要自己设置界限组件。 使用setBounds(..)或setLocation(..)和setSize(..)。

在您的代码中，您设置了首选大小，但这仅与LayoutManager相关，setPreferredSize(..)在布局组件和计算容器的首选大小时使用此大小作为提示。

TL / DR：
将setSize(..)替换为{{1}}，它应该有效。