有关快速帮助，请参见注解：）

public class SongWriter {

  private int song;
  //variable for the number of songs played

  private int royalty;
  //variable for the number of payments

  private int identification_number;
  //id number of the song writer

  public String first_name;
  //string for the first name of songwriter

  public String last_name;
  //string for the last name of the songwriter

  public SongWriter(int myFavSong){
      //define default values for vars above

      this.song = myFavSong;
      //'This' references the Songwriter object not required but useful practice.

  }

  // Lower case first word upcase second : camelCase  
  public int addingSong(int numSongs){
    song = song + numSongs;
    if(song > 100){
      System.out.println("You are a big star!");
     }
     return(song);
  }

  public int requestingCheck(){
    royalty = royalty + 10;
    System.out.println("You just got payed");
    return royalty;
  }
  // The main method shouldn't be nested another class
  public static void main(String[] args){
        //In java because our variables and functions are not static
        //you need a reference to your SongWrite object
        SongWriter songWriter = new SongWriter();

        // Notice I modified your function to take in an int as a param
        songWriter.song = addingSong(5);

        System.out.println(songWriter.song);
  }
}

由于缺乏信息，我们解决你的问题有点困难。请详细地告诉我们你采取了哪些步骤，犯了哪些错误。
从我现在看到的情况来看，由于您使用的是内部类（另一个类中的类），所以应该使其成为静态的：
static class Songwriter{/*your code here*/ } 当你得到这个结果时，你可以通过调用你的外部类在main（）中创建这个类的对象，所以在你的例子中它是： songcode.Songwriter name = new songcode.Songwriter(); 现在，您可以通过使用name.method（）来使用内部类中的方法，例如： name.Requesting_check(); for(int i = 0; i<200; i++){ name.Adding_song(); } 就我个人而言，我会创建一个名为songwriter.java的新java文件，添加一个构造函数并使用它，但这可能不是您在这里测试的；-）
希望它确实能帮助你，请下次提供更详细的信息，这样我们就可以给你一个准确的答案，而不必猜测什么是错的，你想用你的代码实现什么。