Question

我想使用Book类中的方法isLong（）并在BookLolBooks（）中使用它，这是在BookCollection方法中。类BookCollection具有bookList变量。变量bookList是ArrayList类型，包含所有书籍的集合。 ArrayList中的所有对象都是Book类型。

 import java.util.ArrayList;
    public class BookCollection
    {
   ArrayList<Book> bookList = new ArrayList<Book>();

   public BookCollection(){
   bookList.add(new Book(1001-01-141514, "Letones", "CS", 611));
   bookList.add(new Book(1002-01-141424, "Lewis", "CS", 477));
   bookList.add(new Book(1003-01-141434, "Smith", "MATH", 698));
   bookList.add(new Book(1004-01-141444, "Smith", "CS", 617));
   bookList.add(new Book(1005-01-141454, "Brown", "CHEM", 326));
   bookList.add(new Book(1006-01-141464, "Smith", "BIO", 127));
   bookList.add(new Book(1007-01-141474, "Sanket", "CS", 998));
 }
 public String toString()
 {

 }
 public void displayLongBooks()
 {
     System.out.println();
     System.out.println("LONG BOOKS");
     if (isLong() == true)
     System.out.println(bookList);
 }
 public void displayBooksFromAuthor(String author)
 {

 }
 public void displayBooksFromArea(String area)
 {

 }
 public void displayAverageLength()
 {

 }
}




import java.util.*;
import java.io.*;
public class Book
{
    String author;
    String area;
    int isbn;
    int pages;

 public Book (int isbn, String author, String area, int pages)
   {
      this.isbn = isbn;
      this.author = author;
      this.area = area;
      this.pages = pages;     
   }
 public boolean isLong()
   {
     if(pages>600)
     return true;
     else
     return false;
   }
 public String toString()
 {
     return "ISBN: " + this.isbn + "Author: " + this.author
            + "Subject: " + this.area + "Pages: " + this.pages;
 } 
 /**PrintWriter outfile = new PrintWriter (new FileWriter("books.txt"));
 outfile.write("100101141514, Letones, CS, 611");
 outfile.write(100201141424, Lewis, CS, 477);
 outfile.write(100301141434, Smith, MATH, 698);
 outfile.write(100401141444, Smith, CS, 617);
 outfile.write(100501141454, Brown, CHEM, 326);
 outfile.write(100601141464, Smith, BIO, 127);
 outfile.write(100701141474, Sanket, CS, 998);
 outfile.close();**/
}

Answer 1

听起来您需要为bookList（s）迭代Book并为每个Book.isLong()调用public void displayLongBooks() { System.out.println(); System.out.println("LONG BOOKS"); for (Book b : bookList) { // <-- for each Book b in bookList if (b.isLong()) { // no need for == true System.out.println(b); // <-- b, not bookList } } }。使用可能类似

的for-each loop

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在if语句中使用布尔方法时遇到问题

1 个答案: