所以我正在尝试用Java制作一个计算器而且我已经拥有它，以便当你克服123456789或者。按钮，它会将其添加到文本字段。问题是，一旦我添加了6个字符，它将显示“null”。这是我的代码：
import java.awt.EventQueue;
import javax.swing.JFrame;
import javax.swing.JButton;
import javax.swing.JTextField;
import java.awt.event.ActionListener;
import java.awt.event.ActionEvent;
import javax.swing.SwingConstants;
import java.awt.Font;
public class Calculator {
private JFrame frame;
private JTextField textField;
//Variables
private double plus;
private double minus;
private double divide;
private double multiply;
//Check for button clicks
private int plusClick;
private int munisClick;
private int multiplyClick;
private int divideClick;
/**
* Launch the application.
*/
public static void main(String[] args) {
EventQueue.invokeLater(new Runnable() {
public void run() {
try {
Calculator window = new Calculator();
window.frame.setVisible(true);
} catch (Exception e) {
e.printStackTrace();
}
}
});
}
/**
* Create the application.
*/
public Calculator() {
initialize();
}
/**
* Initialize the contents of the frame.
*/
private void initialize() {
frame = new JFrame();
frame.setResizable(false);
frame.setBounds(100, 100, 242, 315);
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.getContentPane().setLayout(null);
JButton equalsButton = new JButton("=");
equalsButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
}
});
equalsButton.setBounds(185, 202, 41, 74);
frame.getContentPane().add(equalsButton);
JButton additionButton = new JButton("+");
additionButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
}
});
additionButton.setBounds(185, 163, 41, 38);
frame.getContentPane().add(additionButton);
JButton subtractionButton = new JButton("-");
subtractionButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
}
});
subtractionButton.setBounds(185, 124, 41, 38);
frame.getContentPane().add(subtractionButton);
JButton divideButton = new JButton("/");
divideButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
}
});
divideButton.setBounds(185, 86, 41, 38);
frame.getContentPane().add(divideButton);
JButton multiplyButton = new JButton("x");
multiplyButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
}
});
multiplyButton.setBounds(185, 49, 41, 37);
frame.getContentPane().add(multiplyButton);
textField = new JTextField();
textField.setHorizontalAlignment(SwingConstants.RIGHT);
textField.setBounds(0, 0, 226, 49);
frame.getContentPane().add(textField);
textField.setColumns(10);
final JButton zeroButton = new JButton("0");
zeroButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText()+zeroButton.getText());
}
});
zeroButton.setBounds(10, 231, 137, 34);
frame.getContentPane().add(zeroButton);
final JButton one = new JButton("1");
one.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + one.getText());
}
});
one.setBounds(10, 193, 41, 34);
frame.getContentPane().add(one);
final JButton two = new JButton("2");
two.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + two.getText());
}
});
two.setBounds(56, 193, 41, 34);
frame.getContentPane().add(two);
final JButton three = new JButton("3");
three.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + three.getText());
}
});
three.setBounds(106, 193, 41, 34);
frame.getContentPane().add(three);
final JButton four = new JButton("4");
four.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + four.getText());
}
});
four.setBounds(10, 153, 41, 34);
frame.getContentPane().add(four);
final JButton five = new JButton("5");
five.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + five.getText());
}
});
five.setBounds(56, 153, 41, 34);
frame.getContentPane().add(five);
final JButton six = new JButton("6");
six.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getSelectedText() + six.getText());
}
});
six.setBounds(106, 153, 41, 34);
frame.getContentPane().add(six);
final JButton seven = new JButton("7");
seven.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + seven.getText());
}
});
seven.setBounds(10, 116, 41, 34);
frame.getContentPane().add(seven);
final JButton eight = new JButton("8");
eight.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + eight.getText());
}
});
eight.setBounds(56, 116, 41, 34);
frame.getContentPane().add(eight);
final JButton nine = new JButton("9");
nine.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + nine.getText());
}
});
nine.setBounds(106, 116, 41, 34);
frame.getContentPane().add(nine);
JButton clearButton = new JButton("Clear");
clearButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText("");
}
});
clearButton.setBounds(10, 67, 87, 38);
frame.getContentPane().add(clearButton);
final JButton decimalButton = new JButton(".");
decimalButton.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e){
textField.setText(textField.getText() + decimalButton.getText());
}
});
decimalButton.setFont(new Font("Tahoma", Font.PLAIN, 20));
decimalButton.setBounds(106, 67, 41, 38);
frame.getContentPane().add(decimalButton);
}
}
如何让它显示所有数字而不给我“null”。
谢谢！
答案 0 :(得分：1)
final JButton six = new JButton("6");
six.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getSelectedText() + six.getText());
}
});
应该是
final JButton six = new JButton("6");
six.addActionListener(new ActionListener() {
public void actionPerformed(ActionEvent e) {
textField.setText(textField.getText() + six.getText());
}
});
由于按下按钮时未选择任何文本，它将返回null，然后将其转换为字符串，然后具有＆＃34; 6＆＃34;附加到它。
答案 1 :(得分：1)
简单。如果您只是将6按钮与其余按钮进行比较，则会注意到您在ActionListener中执行了不同的操作。更改以下内容：
textField.setText(textField.getSelectedText() + six.getText());
到
textField.setText(textField.getText() + six.getText());
此外，我高度建议您在使用空布局遇到问题之前通过A Visual Guide to Layout Managers。