子類toString打印null？ （使用相同的參數爲不同的toStrings）

Question

我想做一個瘋狂的庫遊戲，用戶將輸入5個變量（名詞，形容詞，動詞，副詞，第二名詞），然後將在我的子類中使用不同的「庫」。問題是，當我輸入我的參數時，它將輸出爲空。我確信有一個簡單的方法可以爲不同的toStrings使用相同的輸入，但是我對新的繼承並不確定它的工作原理。

（我看了看其他的toString空的問題，但沒有人跟我的情況相當的工作，或有東西不對它們的構造函數。我相當肯定有什麼錯我的。）

這裏我的短語超：

public class Phrase 
{ 
    private String noun; 
    private String adjective; 
    private String verb; 
    private String adverb; 
    private String noun2; 

    public Phrase (String n, String a, String v, String ad, String n2) 
    { 
     n=noun; 
     a=adjective; 
     v=verb; 
     ad=adverb; 
     n2=noun2; 
    } 

    public String getNoun() 
    {return noun;} 

    public String getAdj() 
    {return adjective;} 

    public String getVerb() 
    {return verb;} 

    public String getAdverb() 
    {return adverb;} 

    public String get2Noun() 
    {return noun2;} 

    //i'll need the get methods in the libs classes and the set methods in the 
    while loop, if user wants to change parameters 

    public void setNoun (String Newnoun) 
    {noun=Newnoun;} 

    public void setAdj (String newAdj) 
    {adjective=newAdj;} 

    public void setVerb (String newVrb) 
    {verb=newVrb;} 

    public void setAdverb (String newAdv) 
    {adverb=newAdv;} 

    public void set2Noun (String newNoun2) 
    {noun2=newNoun2;} 

} 

這裏是我的子類：

public class Obama extends Phrase 
{ 
    public Obama(String noun, String adjective, String verb, String adverb, 
      String noun2) 
    {super (noun, adjective, verb, adverb, noun2);} 

    public String getNoun() 
    {return super.getNoun();} 

    public String getAdj() 
    {return super.getAdj();} 

    public String getVerb() 
    {return super.getVerb();} 

    public String getAdverb() 
    {return super.getAdverb();} 

    public String get2Noun (String n) 
    {return super.get2Noun();} 


    public String toString() 
    { 
     return ("there is a " + super.getAdj() + " " + super.getNoun() +" on the 
       floor! It is " + super.getVerb() +"ing " + super.getAdverb() +". Next to it 
       is a " + super.get2Noun()); 
    } 


} 

這裏是我的司機：

public class Madlibsdriver 
{ 
    static Scanner scan= new Scanner (System.in); 
    public static void main(String[] args) 
    { 

     System.out.print ("Welcome to Mad libs!"); 
     System.out.println(); 
     System.out.println("-------------------------------------------- "); 
     System.out.println("Enter a noun:"); 
     String ip1= scan.nextLine(); 
     System.out.println("Enter an adjective:"); 
     String ip2= scan.nextLine(); 
     System.out.println ("Enter a verb:"); 
     String ip3= scan.nextLine(); 
     System.out.println ("Enter an adverb (ex: angrily) :"); 
     String ip4= scan.nextLine(); 
     System.out.println ("Enter another noun:"); 
     String ip5= scan.nextLine(); 

     Phrase obama= new Obama(ip1, ip2, ip3, ip4, ip5); 

     System.out.println(); 
     System.out.print (obama.toString()); 

    } 

} 

Answer 1

您已經交換了構造函數中的參數，設置了您傳入的值（而不是使用它們來設置本地字段）。使用this關鍵字來捕獲此類錯誤，如

public Phrase (String n, String a, String v, String ad, String n2) 
{ 
    this.noun = n; 
    this.adjective = a; 
    this.verb = v; 
    this.adverb = ad; 
    this.noun2 = n2; 
}