Java Bluej实例不显示打印

Question

我正在使用bluej为用户列表制作一个程序。当我编译和运行代码时，bluej不会给anny提供错误。但是当我创建一个类的新实例时，它看起来什么也没发生。从我的实例向我的终端窗口打印一行不起作用。如何使实例打印显示在终端窗口中？

   import java.util.*;
   import java.text.*;

   public class Main{
       private ArrayList<List> userlists;
       public Main(){
          System.out.print('\f');
          System.out.println("this text will show.");
          newlist("listname");
       }
       public void newlist(String listname){
          System.out.println("this text will show too!");
          List userlist = new List(listname); //terminal does not show lines printed by constructor of List?
          userlists.add(userlist);
          userlist.printSomeText(); //second attempt to print a line, does not show in terminal.
       }
    }

    public class List {
        private String listname;
        public List(String ln) {
            listname = ln;
            System.out.println("this text does not show.");
        }
        public void printSomeText(){
            System.out.println("this text neither.");      
        }
    }

this text will show.
this text will show too!

this text will show.
this text will show too!
this text does not show.
this text neither.

它没有显示anny错误，所以我想知道哪里出错了，如何得到第二个结果，显示这四行。

Answer 1

首先，在同一个Java文件中没有两个public类。

其次，在使用变量或字段之前必须初始化变量，这在您的问题中没有发生。我在你的代码中做了一些修改，这将根据你的工作，也打印第二组行，你想打印。

import java.util.ArrayList;

public class Main {
    private ArrayList<List> userlists;

    public Main() {
        userlists = new ArrayList<List>();
        System.out.print('\f');
        System.out.println("this text will show.");
        newlist("listname");
    }

    public void newlist(String listname) {
        System.out.println("this text will show too!");
        List userlist = new List(listname); // terminal does not show lines
                                            // printed by constructor of List?
        userlists.add(userlist);
        userlist.printSomeText(); // second attempt to print a line, does not
                                    // show in terminal.
    }

    public static void main(String ... args){
        new Main();
    }
}

class List {
    private String listname;

    public List(String ln) {
        listname = ln;
        System.out.println("this text does not show.");
    }

    public void printSomeText() {
        System.out.println("this text neither.");
    }
}