按钮没有出现,空指针异常

Question

我正在学习使用java.swing库.我正在尝试创建一个非常简单的计算器布局.我添加了addNumbers方法.我试图在计算器中显示按钮,我已经用于loops.buttons没有出现我正在获得nullpointerexception.

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

public class Calculator extends JFrame{

    /**
     * @param args
     */
    //dEFINE WIDTH AND HEIGHT
    private static final int WIDTH = 400;
    private static final int HEIGHT = 600;

    //Values for buttons having numbers
    private JButton[] numButton;

    public static void main(String[] args) {
        // TODO Auto-generated method stub

        Calculator myCalculator = new Calculator();

    }

    public Calculator(){
        setTitle("Simple Calculator");
        setSize(WIDTH,HEIGHT);
        setVisible(true);
        setDefaultCloseOperation(EXIT_ON_CLOSE);

        Container Pane = getContentPane();
        Pane.setLayout(new GridLayout(3,3));

        //Add numbers to screen now
        addNumbers(Pane);



    }

    //Function to add numbers on screen
    public void addNumbers(Container P){
        for(int i = 1; i <= 9; i++){
            numButton[i] = new JButton(String.valueOf(i));
            P.add(numButton[i]);
        }
    }

}

Answer 1

您需要初始化您的数组:

private JButton[] numButton = new JButton[10];

这里的10允许您的阵列中有10个空格.