java - 警告 : static method should be accessed in a static way

Question

我正在学习Java，我打算创建一个计算器Java 小程序，它具有加、除、乘和重置的功能。得到一些警告标志:

The static method valueOf(double) from the type String should be accessed in a static way

虽然计算器在工作。但请就如何避免此警告标志以及我可以对编码进行哪些改进寻求您的专业知识。

CalEngine 类，包括监听器、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();
    }
}

Answer 1

这是有问题的代码行:

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

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

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