Что не так с моей java-программой?

Question

Я пытаюсь создать программу, которая изменяет мою первоначальную историю, если три «Рассказчика» внесут изменения в оригинал. Однако, когда я пытаюсь запустить TellStory, программа только печатает «nullnullnull» для окончательной истории пересказки. Что я сделал не так? Большое спасибо за ваше время :)

public class TellStory{ 
public String story; 
public static void main(String[]args){ 
    String story="The three little pigs went shopping for lettuce. When they arrived at   the grocery store, they found they had forgotten their money. They asked the manager if they could have some credit, but he refused. The three little pigs saw their friend, Mr. Turtle, and he agreed to give them a loan. They went home happy and had a wonderful meal!"; 
    System.out.println("Welcome to my Story"); 
    System.out.println(""); 
    System.out.println("Initial Story:"); 
    System.out.println(story); 
    System.out.println(""); 

    Storyteller1 Frank=new Storyteller1(); 
    Storyteller2 John=new Storyteller2(); 
    Storyteller3 Jake=new Storyteller3(); 

    String storyRetoldByFrank=Frank.getStory1(); 
    String storyRetoldByJohn=John.getStory2(); 
    String storyRetoldByJake=Jake.getStory3(); 

    String FinalRetoldStory=storyRetoldByFrank+storyRetoldByJohn+storyRetoldByJake; 

    System.out.println("Final Retold Story:"); 
    System.out.println(FinalRetoldStory); 
    } 
} 

public class Storyteller1 extends TellStory{ 
public String story1; 
public String retellStory(String story1){ 
    int startIndex1=story.indexOf("three little pigs went"); 
    String subStr1=story.substring(startIndex1,startIndex1+17); 
    String subStr2=story.replaceAll(subStr1,"four chickens"); 

    int startIndex2=story.indexOf("lettuce. When"); 
    String subStr3=story.substring(startIndex2,startIndex2+8); 
    String subStr4=story.replaceAll(subStr3,"raisins"); 

    int startIndex3=story.indexOf("grocery store, they"); 
    String subStr5=story.substring(startIndex3,startIndex3+14); 
    String subStr6=story.replaceAll(subStr5,"mall"); 

    int startIndex4=story.indexOf("money. They"); 
    String subStr7=story.substring(startIndex4,startIndex4+6); 
    String subStr8=story.replaceAll(subStr7,"friend"); 

    story1=subStr2+" went shopping for "+subStr4+". "+"When they arrived at the "+subStr6+", they found they had forgotten their "+subStr8+"."; 
    return story1; 
    } 
    public String getStory1(){ 
    return story1; 
    } 
} 

public class Storyteller2 extends TellStory{ 
public String story2; 
public String retellStory(String story2){ 
    int startIndex5=story.indexOf("manager"); 
    String subStr9=story.substring(startIndex5,startIndex5+8); 
    String subStr10=story.replaceAll(subStr9,"security guard"); 

    int startIndex6=story.indexOf("some credit"); 
    String subStr11=story.substring(startIndex6,startIndex6+12); 
    String subStr12=story.replaceAll(subStr11,"a phone"); 

    story2="They asked the "+subStr11+" if they could have "+subStr11+", but he refused."; 
    return story2; 
    } 
    public String getStory2(){ 
    return story2; 
    } 
} 

public class Storyteller3 extends TellStory{ 
public String story3; 
public String retellStory(String story3){ 
    int startIndex7=story.indexOf("friend"); 
    String subStr13=story.substring(startIndex7,startIndex7+7); 
    String subStr14=story.replaceAll(subStr13,"nemesis"); 

    int startIndex8=story.indexOf("Mr. Turtle"); 
    String subStr15=story.substring(startIndex8,startIndex8+11); 
    String subStr16=story.replaceAll(subStr15,"Fearsome Fox"); 

    int startIndex9=story.indexOf("loan"); 
    String subStr17=story.substring(startIndex9,startIndex9+5); 
    String subStr18=story.replaceAll(subStr17,"ride"); 

    int startIndex10=story.indexOf("happy and"); 
    String subStr19=story.substring(startIndex10,startIndex10+10); 
    String subStr20=story.replaceAll(subStr19,"with Fearsome Fox - he"); 

    story3="The three little pigs saw their "+subStr14+","+subStr16+" and he agreed to  give them a "+subStr18+". They went home "+subStr20+"had a wonderful meal!"; 
    return story3; 
    } 
    public String getStory3(){ 
    return story3; 
    } 
} 

Answer 1

1. Никто не вызывая метод retellStory, поэтому ничего не создается ...
2. Значения story1, story2 и story3 никогда не быть присвоены какие-либо значения. ..
3. поле экземпляра story, который осуществляется доступ к Storyteller1, Storyteller2, Storyteller3 никогда не присваивается значение и будет null, вызывая NullPointerException

Answer 2

Метод retellStory никогда не вызывается StoryTeller.

Добавить метод retellStory конструктору для каждого StoryTeller или добавить вызов метода после инициализации каждого StoryTeller