當我運行該程序時，GUI 就會出現(xiàn)。當我單擊按鈕時，屏幕上沒有任何內(nèi)容。在我的操作執(zhí)行方法中，屏幕無法解析，因為我尚未在方法中聲明它。screen 在我的 init 方法的開頭聲明。我不明白第二種方法中的代碼將如何應用于第一種方法（GUI）。有小費嗎？import acm.program.*;import javax.swing.*;import java.awt.*; // for graphics import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import acm.gui.*;public class Calculator extends DialogProgram implements ActionListener{ public void init() { JButton b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,bm,bd,ba,bs,bdec,bc; DoubleField screen; //create a panel JPanel P= new JPanel(); // main panel JPanel P1= new JPanel(); // panel for buttons JPanel P2= new JPanel(); // panel for screen // adding panel to dialog box add(P); // main panel P.add(P2); // adding screen P.add(P1); // adding panel of buttons // set panel color P.setBackground(Color.yellow); // grid layout for buttons P1.setLayout(new GridLayout(4,4,4,4)); // layout for button panel P.setLayout(new GridLayout(2,1)); // layout for main panel // create screen screen = new DoubleField(); // creating screen screen.setPreferredSize(new Dimension(200,40)); // setting screen size screen.setEditable(false); // screen can not be edited // integer buttons b0 = new JButton("0"); b1 = new JButton("1"); b2 = new JButton("2"); b3 = new JButton("3"); b4 = new JButton("4"); b5 = new JButton("5"); b6 = new JButton("6"); b7 = new JButton("7"); b8 = new JButton("8"); b9 = new JButton("9"); // operator buttons bm = new JButton("*"); bd= new JButton("/"); ba = new JButton("+"); ba.addActionListener(this); bs = new JButton("-"); // decimal button bdec = new JButton("."); // clear button bc = new JButton("C"); }
1 回答
互換的青春
TA貢獻1797條經(jīng)驗 獲得超6個贊
將所有 GUI 組件的變量聲明移出init()方法，但仍在Calculator類內(nèi)，這樣它們對于actionPerformed可能需要訪問它們的其他方法（例如 ）是可見的：
public class Calculator extends DialogProgram implements ActionListener{
JButton b0,b1,b2,b3,b4,b5,b6,b7,b8,b9,bm,bd,ba,bs,bdec,bc;
DoubleField screen;
JPanel P, P1, P2;
public void init() {
P= new JPanel(); // main panel
P1= new JPanel(); // panel for buttons
P2= new JPanel(); // panel for screen
// continue setting up the rest of the GUI...
}
public void actionPerformed (ActionEvent e) {
String clicked = e.getActionCommand();
if (clicked.equals("ba")) {
screen.setText("+");
}
}
}
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