java 作业问题,求大神帮忙

当我运行选择 n 的时候就弹出,显示错误了 --------------------编程问答-------------------- 是不是小了点！！！ --------------------编程问答-------------------- 问题解决了,但是还有其他问题,我发一下 --------------------编程问答--------------------             case 5:
                    String dbchoice = "";
                    boolean dbempty = false;
                    do
                    {
                        System.out.println("Do you want to delete songs from database?（y/n)");
                        dbchoice = console.next();
                        dbchoice = dbchoice.toLowerCase();
                        System.out.println("Select the song you want to delete.");
                        int songNumber = console.nextInt();
                        database.deletSong(songNumber);
                        System.out.println("No."+songNumber+" song has already deleted from database.");                    
                        database.resize();
                        if (playlist[listnumber-1].getNum()==0)  
                        {
                            dbempty = true;
                            System.out.println("Database is empty.");
                        }
                    }while(dbchoice.equals("n")||dbempty);
                    break;


当我运行这一段的时候,另外一个class报错
    public void deletSong(int deletNum)
    {
        for (int i = deletNum-1; i < logicalSize; i++)
           { 
               allSongs[i] = allSongs[i+1];
            }
        logicalSize--;
        song.decrease();
        
    }
    
这一段最后一句报错
java.lang.NullPointerException:
null

--------------------编程问答-------------------- 你的空指针异常后面应该会打印一些堆栈信息，告诉你那个类多少行出错了，建议把这个详细的错误日志，以及出错的类文件都发一下

补充：Java ,  Java相关