关于java：错误：在类TextBook中找不到主要方法，请将main方法定义为：public static void main（String [] args）

Error: Main method not found in class TextBook, please define the main method as: public static void main(String[] args)

我试着编译它，它说没有错误。但当我运行程序时，它会说：

Error: Main method not found in class TextBook, please define the main
method as: public static void main(String[] args)

所以当我添加public static void main时，整个程序有很多错误。

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import java.util.*;

public class Book

{
private int pageNum;
private String title;
Date today = new Date();

public Book(int pn, String name)
{
pageNum = pn;
title = name;
}

//Setter/Getter for pageNum
public int getpageNum()
{
return pageNum;
}

public void setpageNum(int pn)
{
pageNum = pn;
}
//Setter/Getter for Title
public String getTitle()
{
return title;
}

public void setTitle(String name)
{
title = name;
}

public void display()
{
System.out.println("Book.java" +"
by Tyler" + today);
System.out.println("Book Title:" + title +"
Number of Pages:" + pageNum);
}
}

用于bookbook.java

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public class TextBook extends Book
{
private String gradeLevel;

public TextBook(int pageNum, String title, String gl)
{
super(pageNum, title);
gradeLevel = gl;
}

//Setter/Getter for gradeLevel
public String getGradeLevel()
{
return gradeLevel;
}

public void setGradeLevel(String g)
{
gradeLevel = g;
}

public void display()
{
super.display();
System.out.println("Grade Level:" + gradeLevel);
}

}

用于demobook.java

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public class DemoBook
{
public static void main(String[] args)
{
Book oneBook = new Book(250,"Awesome Story");
TextBook oneTextBook = new TextBook(350,"Awesomer Story","12");

oneBook.display();
oneTextBook.display();
}
}