java - 无法从 ActionPerformed 调用构造函数组件

Question

执行bottomLabel.setVisible(true);时，我遇到 Unresolved 编译问题:

The type Assignment1 must implement the inherited abstract method ActionListener.actionPerformed(ActionEvent)

就像我应该创建一个新变量，因为它无法从构造函数中读取。我的错误在哪里？这是尽可能简化的代码:

public class Assignment1 extends JFrame implements ActionListener{

//declare variables
int x= 101;
int low = 0;
int high = 100;
int guess = (high + low) / 2;
int counter = 0;

private static final long serialVersionUID = 1L;

//main method
//...some code... 


//constructor
public Assignment1(){
//...some code... 

    //declare buttons
    JButton correct = new JButton("correct!");

    //add buttons
    //...some code... 

    //declare TextField and Labels
    JTextField numberTextField = new JTextField(20); 
    JLabel topLabel = new JLabel("T"); 
    JLabel bottomLabel = new JLabel("G"); 

    //add TextField and Labels and position them on the layout
        //...some code... 
    bottomLabel.setBounds(110, 300, 400, 20);
    add(bottomLabel);
    bottomLabel.setVisible(false);

    //add ActionListener to each button
//...some code... 
    correct.addActionListener(this);

}

@Override
//define ActionPerformed when an Event is parsed
public void actionPerformed(ActionEvent e) {
    String buttonClicked = e.getActionCommand();

    if(buttonClicked.equals("Yes, correct!")){
        System.out.println("correct");
        bottomLabel.setVisible(true);
    }

}
}   

这是完整的堆栈跟踪:

at Assignment1.Assignment1.actionPerformed(Assignment1.java:12)
at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
at java.awt.Component.processMouseEvent(Unknown Source)
at javax.swing.JComponent.processMouseEvent(Unknown Source)
at java.awt.Component.processEvent(Unknown Source)
at java.awt.Container.processEvent(Unknown Source)
at java.awt.Component.dispatchEventImpl(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
at java.awt.Container.dispatchEventImpl(Unknown Source)
at java.awt.Window.dispatchEventImpl(Unknown Source)
at java.awt.Component.dispatchEvent(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.awt.EventQueue$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

bottomLabel 仅在构造函数内可见，因为它未在类级别声明。

在类级别声明它(就像您对 x、low、high 等所做的那样)以使其正常工作:

public class Assignment1 extends JFrame implements ActionListener {

    // declare variables
    int x = 101;
    int low = 0;
    int high = 100;
    int guess = (high + low) / 2;
    int counter = 0;
    JLabel bottomLabel;  // <==


    public Assignment1() {
        // [...] other assignments
        bottomLabel = new JLabel("Game Over, your number is NN, i got it in N times. Wanna play again?");
        // [...] rest of class