如何从存储在ArrayList中的方法返回toString方法

Question

谢谢

代码如下：

import java.util.ArrayList;

public class TestTextbooks {  

        public static void main(String[] args) {
            Textbook java101 = new ProgrammingTextbook("Java101","Dr Migoreng",1331,"Java");
            Textbook python201 = new ProgrammingTextbook("Python201","Dr Karl",112,"Python");
            Textbook fluidMechanics = new EngineeringTextbook("Fluids101","Dr Brisbane",122,"GIS","Fluid Mechanics");
            Textbook modelling101 = new EngineeringTextbook("Modelling101","Dr Suzuki",322,"WaterGems","Water Modelling");

      ArrayList books = new ArrayList();
      books.add(java101); 
      books.add(python201); 
      books.add(fluidMechanics);
      books.add(modelling101);

      System.out.println("" + books.toString());
            }    
    }

public class ProgrammingTextbook extends Textbook {
    private String language;
    private String title;
    private String author;
    private int pages;


    public ProgrammingTextbook (){
    }

        //overloaded constructor
    public ProgrammingTextbook (String title, String author,int pages,String language){
        this.title = title;
        this.author = author;
        this.pages = pages;
        this.language=language;
    }
    //set method for overloaded constructor
    public void setProgrammingTextBook (String title, String author,int pages,String language){
        setLanguage(language);
    }
     //individual set methods
    public void setLanguage(String language){
        this.language = language;
    }
    //individual get methods
    public String getLanguage(){
        return language;
    }  
    public String toString(String title, String author,int pages,String language){
        return title + "/" + author + "/" + pages + "/" + language;
    }

}

public class EngineeringTextbook extends Textbook {
    private String language;
    private String subject;
        //default constructor (probs shouldn't actually have values)
        public EngineeringTextbook (){
    }
    //overloaded constructor
    public EngineeringTextbook (String title, String author,int pages,String language,String subject){
        this.title = title;
        this.author = author;
        this.pages = pages;
        this.language=language;
        this.subject=subject;
    }
    //set method for overloaded constructor
    public void setEngineeringTextBook (String title, String author,int pages){
        setLanguage(language);
        setSubject(subject);
    }
        //individual set methods
    public void setLanguage(String language){
        this.language = language;
    }
    public void setSubject(String subject){
        this.subject = subject;
    }

    //inbdividual get methods
    public String getLanguage(){
        return language;
    }
    public String getSubject(){
        return subject;
    }

    //toString method
    public String toString(String title, String author,int pages,String language,String subject){
        return title + "/" + author + "/" + pages + "/" + language + "/" + subject;
    }
}

public abstract class Textbook {

    protected String title;
    protected String author;
    protected int pages;

    //default constructor (Don't really need to add null for all values but put in to show it is a default constructor
    public Textbook (){
        this.title = null;
        this.author = null;
        this.pages = 0;
    }
    //overloaded constructor
    public Textbook (String title, String author,int pages){
        this.title = title;
        this.author = author;
        this.pages = pages;
    }
    //individual set methods
    public void setTitle(String title){
        this.title = title;
    }
    public void setAuthor(String author){
        this.author = author;
    }
    public void setPages(int pages){
        this.pages = pages;
    }
    //individual get methods
    public String getTitle(){
        return title;
    }
    public String getAuthor(){
        return author;
    }
    public int getPages(){
        return pages;
    }
    //abstract toString method
    public String toString(String title, String author,int pages){
       return title + "/" + author + "/" + pages;
    }   
}

Answer 1

object.ToString()不接受任何参数。当您未能正确重写方法时，请使用@override批注来捕获它。

@Override
public String toString() {
    return title + "/" + author + "/" + pages + "/" + language;
}

而且

@Override
public String toString() {
   return title + "/" + author + "/" + pages;
}   

等等。