如何遍历数组列表并打印包含单词的索引？

Question

I want to know how to iterate through a arraylist and print out all the index's containing a number that the user put in the scanner. If the number is not in the scanner then it would print out value is not in the list. I have two classes in my program.

Below is my Entertainment Class:

         public class Real_Entertainment 
      {
            String BookName; 
            String Author; 
            double Rating; 
            int Purchases;


public Real_Entertainment(String BookName, String Author, double Rating, int Purchases)
{
    this.BookName = BookName;
    this.Author = Author;
    this.Rating = Rating;
    this.Purchases = Purchases;
}
public void setBookName(String BookName)
{
    this.BookName = BookName;
}
public void setAuthor (String Author )
{
    this.Author = Author;
}
public void setRating (double Rating)
{
    this.Rating = Rating;
}
public void setPurchased (int Purchases)
{
    this.Purchases = Purchases;
}


    }

Below is the main class that contains the arraylist:

    import java.util.Scanner;
    import java.util.ArrayList;
    public class Real_Main 
    {




        public static void main(String[] args) 
        {


    ArrayList<Real_Entertainment> print = new ArrayList<Real_Entertainment>();
    Real_Entertainment Book1 = new Real_Entertainment("The Nickel Boys ", "Colson Whitehead", 4.3, 500000);
    Real_Entertainment Book2 = new Real_Entertainment("Olive, Again", "Elizabeth Strout", 6, 321000);
    Real_Entertainment Book3 = new Real_Entertainment("Gingerbread", "Helen Oyeyemi", 2, 681000);
    Real_Entertainment Book4 = new Real_Entertainment("On Earth We're Briefly Gorgeous", "Ocean Vuong", 2, 421000);

    print.add(Book1);
    print.add(Book2);
    print.add(Book3);
    print.add(Book4);



 findPrimitiveValue(print);


}

public static void findPrimitiveValue(ArrayList<Real_Entertainment> print)
{
        Scanner scanner = new Scanner(System.in);
        System.out.println("Enter a Numeric Value:" );
        int input = scanner.nextInt();
        boolean foundInfo = false;
        for(int i = 0; i < print.size(); i++)
        {
            if(print.get(i).() == input || print.get(i).() == input)
            {
                System.out.println("This is the information found: " );
                System.out.println()
            }
        }

}

   }

I have tried to set the value of the purchases = to the value that the user inputted I kept getting an error.

Answer 1

I refactored your code for

• class, field and parameter names according to conventions,
• turning your Book class into a Java Bean which also has a toString() method for easy printing,
• using less cryptic names in general,
• using Java streams for nicer collection handling.

I also added an example of how you can eg search for an exact match in number of purchases for a book. I also added an additional book with the same number of purchases so we can see more than one search result.

Data class:

package de.scrum_master.stackoverflow.q60461642;

public class Book {
  private String name;
  private String author;
  private double rating;
  private int purchases;

  public Book(String name, String author, double rating, int purchases) {
    this.name = name;
    this.author = author;
    this.rating = rating;
    this.purchases = purchases;
  }

  @Override
  public String toString() {
    return "Book{" +
      "name='" + name + '\'' +
      ", author='" + author + '\'' +
      ", rating=" + rating +
      ", purchases=" + purchases +
      '}';
  }

  public String getName() {
    return name;
  }

  public void setName(String name) {
    this.name = name;
  }

  public String getAuthor() {
    return author;
  }

  public void setAuthor(String author) {
    this.author = author;
  }

  public double getRating() {
    return rating;
  }

  public void setRating(double rating) {
    this.rating = rating;
  }

  public int getPurchases() {
    return purchases;
  }

  public void setPurchases(int purchases) {
    this.purchases = purchases;
  }
}

Driver application:

package de.scrum_master.stackoverflow.q60461642;

import java.util.Arrays;
import java.util.List;
import java.util.Scanner;

public class Application {
  private static List<Book> books = Arrays.asList(
    new Book("The Nickel Boys", "Colson Whitehead", 4.3, 500000),
    new Book("Olive, Again", "Elizabeth Strout", 6, 321000),
    new Book("Gingerbread", "Helen Oyeyemi", 2, 681000),
    new Book("On Earth We're Briefly Gorgeous", "Ocean Vuong", 2, 421000),
    new Book("Perfume", "Patrick Süskind", 6, 500000)
  );

  public static void main(String[] args) {
    printBooks();
    findBooksByNumberOfPurchases();
  }

  private static void printBooks() {
    System.out.println("Books list:");
    books.stream().forEach(System.out::println);
    System.out.println("\n");
  }

  private static void findBooksByNumberOfPurchases() {
    Scanner scanner = new Scanner(System.in);
    System.out.println("Enter the number of purchases to search for:");
    int input = scanner.nextInt();
    books.stream()
      .filter(book -> book.getPurchases() == input)
      .forEach(System.out::println);
  }
}

Console log:

Books list:
Book{name='The Nickel Boys', author='Colson Whitehead', rating=4.3, purchases=500000}
Book{name='Olive, Again', author='Elizabeth Strout', rating=6.0, purchases=321000}
Book{name='Gingerbread', author='Helen Oyeyemi', rating=2.0, purchases=681000}
Book{name='On Earth We're Briefly Gorgeous', author='Ocean Vuong', rating=2.0, purchases=421000}
Book{name='Perfume', author='Patrick Süskind', rating=6.0, purchases=500000}


Enter the number of purchases to search for:
500000
Book{name='The Nickel Boys', author='Colson Whitehead', rating=4.3, purchases=500000}
Book{name='Perfume', author='Patrick Süskind', rating=6.0, purchases=500000}