java - 警告:应该以静态方式访问静态方法

我正在学习Java，并且计划创建一个具有加，除，乘和重设功能的计算器Java小程序。得到了一些警告信号：


类型为String的静态方法valueOf（double）应该以静态方式访问


计算器正在运行。但是，请您寻求有关如何避免这种警告信号以及我可以对编码进行哪些改进的专业知识。

CalEngine类包括侦听器，数学函数。

public class CalEngine implements ActionListener{

    Calculator parent;
    double current=0;
    double prevnum=0;
    double totalnum=0;
    int funct=0;
    String equalnum;
    public CalEngine(Calculator parent) {
        this.parent = parent;
    }


    public void actionPerformed(ActionEvent e) {

    JButton src = (JButton) e.getSource();
    String  cbuttonlabel = src.getText();
    if(cbuttonlabel.equals("+"))
        {       clearscreen();
                funct = 1;      }
    else if(cbuttonlabel.equals("-"))
    {       clearscreen();
            funct = 2;          }
    else if(cbuttonlabel.equals("/"))
    {       clearscreen();
            funct = 3;          }
    else if(cbuttonlabel.equals("="))
    {   equal();                }
    else if(cbuttonlabel.equals("Reset"))
    {   prevnum = 0;
        current = 0;
        totalnum =0;
        clearscreen();
    }
    else
        {
        prevnum = current;
        current = Double.parseDouble(cbuttonlabel);
        parent.setScreen(cbuttonlabel);
        }
    }

    private void equal() {
        if(funct == 1)
        {
            add();
        }
        else if(funct == 2)
        {
            minus();
        }
        else if(funct == 3)
        {
            divide();
        }
        parent.setScreen(equalnum.valueOf(totalnum));
        totalnum =0;
    }

    private void minus() {
        totalnum = prevnum-current;}

    private void divide() {
        totalnum = prevnum/current; }

    private void clearscreen() {
        parent.setScreen("");   }

    private void add() {
        totalnum = current + prevnum;
    }

}



Calculator UI

public class Calculator {

    JPanel ova;
    JPanel pan;
    JTextField screen;
    JButton b1;
    JButton b2;
    JButton b3;
    JButton b4;
    JButton b5;
    JButton b6;
    JButton b7;
    JButton b8;
    JButton b9;
    JButton b0;
    JButton bplus;
    JButton bequal;
    JButton bminus;
    JButton bdivide;
    JButton breset;

    Calculator(){

        ova = new JPanel();
        BorderLayout bl = new BorderLayout();
        ova.setLayout(bl);

        screen = new JTextField(300);
        ova.add("North",screen);

        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");
        b0 = new JButton("0");
        bplus = new JButton("+");
        bequal = new JButton("=");
        bminus = new JButton("-");
        bdivide = new JButton("/");
        breset = new JButton("Reset");

        pan = new JPanel();
        GridLayout gl = new GridLayout(5,3);
        pan.setLayout(gl);

        pan.add(b1);
        pan.add(b2);
        pan.add(b3);
        pan.add(b4);
        pan.add(b5);
        pan.add(b6);
        pan.add(b7);
        pan.add(b8);
        pan.add(b9);
        pan.add(b0);
        pan.add(bplus);
        pan.add(bequal);
        pan.add(bminus);
        pan.add(bdivide);
        pan.add(breset);

        ova.add("Center",pan);

        JFrame jf = new JFrame("Calculator");

        jf.setContentPane(ova);
        jf.setVisible(true);
        jf.setSize(500,500);

        CalEngine calcEngine = new CalEngine(this);
        b0.addActionListener(calcEngine);
        b1.addActionListener(calcEngine);
        b2.addActionListener(calcEngine);
        b3.addActionListener(calcEngine);
        b4.addActionListener(calcEngine);
        b5.addActionListener(calcEngine);
        b6.addActionListener(calcEngine);
        b7.addActionListener(calcEngine);
        b8.addActionListener(calcEngine);
        b9.addActionListener(calcEngine);
        bplus.addActionListener(calcEngine);
        bequal.addActionListener(calcEngine);
        bminus.addActionListener(calcEngine);
        bdivide.addActionListener(calcEngine);
        breset.addActionListener(calcEngine);
    }


    public static void main(String[] args)
    {
        new Calculator();

    }


    public void setScreen(String wee) {

        screen.setText(wee);
    }

    public String getScreen() {

        return screen.getText();
    }
}

最佳答案

这是有问题的代码行：

parent.setScreen(equalnum.valueOf(totalnum));

您正在对String对象（valueOf）的实例调用静态方法equalnum。您应该改为在类本身上调用它。

parent.setScreen(String.valueOf(totalnum));