这个问题在这里已经有答案了：

“找不到符号”或“无法解析符号”错误是什么意思(15个答案）
上个月关门了。
如果我编译这个，我会得到setdefaultcloseoperation、setsize和setvisible的“找不到符号”错误。我的问题是我不明白为什么。这是我家庭作业的一部分。但因为这个问题，我甚至不能开始下一部分

//AdderSubtracterFrame.java
//This class displays a Frame which can add or subtract two numbers
import javax.swing.JFrame;
public class AdderSubtracterProgram
{
    public static void main(String [] args)
    {
        AdderSubtracterFrame frame1 = new AdderSubtracterFrame("Adder and Subtracter");

        frame1.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame1.setSize(400,100);
        frame1.setVisible(true);
    }
}

我添加addersubtracterframe代码两个类在同一个项目中。这个项目是做一个计算器

//AdderSubtracterFrame.java
//This class displays a Frame which can add or subtract two numbers

import javax.swing.JFrame;
import javax.swing.JTextField;
import javax.swing.JButton;
import javax.swing.JPanel;

import java.awt.GridLayout;
import java.awt.FlowLayout;

public class AdderSubtracterFrame
{
    private JTextField num1TextField;
    private JTextField num2TextField;
    private JTextField resultTextField;

    private JButton clearButton;
    private JButton addButton;
    private JButton subtractButton;
    private JButton buttonPanel;

    //Constructor
    public AdderSubtracterFrame(String title)
    {
        //Set the title of the AdderSubtracterFrame by
        //using the superclass JFrame constructor
        super();

        //Set the JFrame to be a 2*2 Grid
        //Set a gap of 5pixels between each row and column.
        setLayout(new GridLayout(2,2,5,5));

        //Create and instance of the components appearing in the 2*2 grid
        num1TextField = new JTextField("0",5);//Begin with 0
        num2TextField = new JTextField("0",5);//Begin with 0
        resultTextField = new JTextField((5));//Begin empty
        buttonPanel = getButtonPanel();

        //Add components to 2*2 Grid
        add(num1TextField);
        add(num2TextField);
        add(resultTextField);
        add(buttonPanel);
    }

    //Create and return a panel containing the buttons
    private JPanel getButtonPanel()
    {
        JPanel myPanel = new JPanel();
        myPanel.setLayout(new FlowLayout());

        //Create an instance of each button
        addButton = new JButton("+");
        subtractButton = new JButton("-");
        clearButton = new JButton("CLEAR");

        //Add the 3button to myPanel
        myPanel.add(addButton);
        myPanel.add(subtractButton);
        myPanel.add(clearButton);

        return myPanel;

    }
}