报错在类中找不到主方法, 请将主方法定义为: public static void main(String[] args) 代码里面要怎么改

import java.io.File;
import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.IOException;
import java.io.UnsupportedEncodingException;

public class sss {
File f=new File("d://","test.txt");
FileInputStream fileInputStream;
FileOutputStream fileOutputStream;
public String read(){
String s=null;
try {
int size=0;
byte[] buffer=new byte[1024];
fileInputStream=new FileInputStream(f);
while((size=fileInputStream.read(buffer))!=-1){
s=new String(buffer,"utf-8");
System.out.println(s);
}
}catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
try {
fileInputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} return s;
}
public Boolean write(String str){
try {byte[] userbname=str.getBytes("utf-8");
fileOutputStream=new FileOutputStream(f,true);
fileOutputStream.write(userbname,0, userbname.length);
}catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (UnsupportedEncodingException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}finally{
try {
fileOutputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
return true;

}public void a(){
this.write("Welcome to Java world");
this.read();
}
}

一个类中需要有程序执行的入口，例如main方法。把a()方法换成main方法，其他方法没问题如下：

public class Sss {

    File f = new File("d://", "test.txt");
    FileInputStream fileInputStream;
    FileOutputStream fileOutputStream;

    public String read()() {
        String s = null;
        try {
            int size = 0;
            byte[] buffer = new byte[1024];
            fileInputStream = new FileInputStream(f);
            while ((size = fileInputStream.read(buffer)) != -1) {
                s = new String(buffer, "utf-8");
                System.out.println(s);
            }
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                fileInputStream.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return s;
    }

    public Boolean write(String str) {
        try {
            byte[] userbname = str.getBytes("utf-8");
            fileOutputStream = new FileOutputStream(f, true);
            fileOutputStream.write(userbname, 0, userbname.length);
        } catch (FileNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (UnsupportedEncodingException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                fileOutputStream.close();
            } catch (IOException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return true;

    }

    public static void main(String[] args) {

        Sss s1 = new Sss();

        s1.write("Welcome to Java world");
        s1.read();
    }

}

运行结果：

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