Класс Bean для программирования на Java

Сортировка массива

Java 8 Функциональный Компаратор

Java 8 представила новые методы в интерфейсе Comparator, который упрощает сравнение с объектами. Я хочу отсортировать свои книги по номеру ISBN. Поскольку строка имеет естественный порядок, я могу сообщить методу сортировки, какой компаратор использовать, следующим образом.

Arrays.sort(myBooks, comparing(Book::getIsbn)); // Comparable function

Посмотрите тестовую программу чуть ниже, чтобы увидеть, как работают Comparable и Comparator.

Полный Боб

Вот окончательный вариант боба Book.

mport java.io.Serializable;
import java.util.Objects;

public class Book implements Serializable, Comparable<Book> {

    private String isbn;
    private String title;
    private String author;
    private String publisher;
    private int pages;

    /**
     * Default constructor
     */
    public Book() {
        this.isbn = "";
        this.title = "";
        this.author = "";
        this.publisher = "";
        this.pages = 0;
    }

    /**
     * Non-default constructor
     *
     * @param isbn
     * @param title
     * @param author
     * @param publisher
     * @param pages
     */
    public Book(final String isbn, final String title, final String author, final String publisher, final int pages) {
        this.isbn = isbn;
        this.title = title;
        this.author = author;
        this.publisher = publisher;
        this.pages = pages;
    }

    public String getIsbn() {
        return isbn;
    }

    public void setIsbn(final String isbn) {
        this.isbn = isbn;
    }

    public String getTitle() {
        return title;
    }

    public void setTitle(final String title) {
        this.title = title;
    }

    public String getAuthor() {
        return author;
    }

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

    public String getPublisher() {
        return publisher;
    }

    public void setPublisher(final String publisher) {
        this.publisher = publisher;
    }

    public int getPages() {
        return pages;
    }

    public void setPages(final int pages) {
        this.pages = pages;
    }

    @Override
    public String toString() {
        return "Book{" + "isbn=" + isbn + ", title=" + title + ", author=" + author + ", publisher=" + publisher + ", pages=" + pages + '}';
    }

    @Override
    public int hashCode() {
        int hash = 7;
        hash = 61 * hash + Objects.hashCode(this.isbn);
        hash = 61 * hash + Objects.hashCode(this.title);
        hash = 61 * hash + Objects.hashCode(this.author);
        hash = 61 * hash + Objects.hashCode(this.publisher);
        hash = 61 * hash + this.pages;
        return hash;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj) {
            return true;
        }
        if (obj == null) {
            return false;
        }
        if (getClass() != obj.getClass()) {
            return false;
        }
        final Book other = (Book) obj;
        if (this.pages != other.pages) {
            return false;
        }
        if (!Objects.equals(this.isbn, other.isbn)) {
            return false;
        }
        if (!Objects.equals(this.title, other.title)) {
            return false;
        }
        if (!Objects.equals(this.author, other.author)) {
            return false;
        }
        if (!Objects.equals(this.publisher, other.publisher)) {
            return false;
        }
        return true;
    }

    /**
     * Natural comparison method for Title
     *
     * @param book
     * @return negative value, 0, or positive value
     */
    @Override
    public int compareTo(Book book) {
        return this.title.compareTo(book.title);
    }
}

// Required for Arrays.sort
import java.util.Arrays;
// Required by the Comparator function
import static java.util.Comparator.comparing;

public class BeanTester {

    /**
     * Here is where I am testing my comparisons
     *
     */
    public void perform() {
        // Lets create four books
        Book b0 = new Book("200", "Xenon", "Hamilton", "Harcourt", 99);
        Book b1 = new Book("500", "Boron", "Bradbury", "Prentice", 108);
        Book b2 = new Book("300", "Radon", "Heinlein", "Thompson", 98);
        Book b3 = new Book("404", "Argon", "Campbell", "Hachette", 102);

        // Using Comparable to compare two books
        System.out.println("Value returned by Comparable");
        System.out.println(b0.getTitle() + " compared to " + b1.getTitle() + ": "
                + b0.compareTo(b1));
        System.out.println();

        // Using Comparator to compare two books
        System.out.println("Value returned by Comparator");
        BookPageComparator bookPageComparator = new BookPageComparator();
        System.out.println(b0.getPages() + " compared to " + b1.getPages() + ": "
                + bookPageComparator.compare(b0, b1));
        System.out.println();

        // Create an array we can sort
        Book[] myBooks = new Book[4];
        myBooks[0] = b0;
        myBooks[1] = b1;
        myBooks[2] = b2;
        myBooks[3] = b3;
        System.out.println("Unsorted");
        displayBooks(myBooks);

        System.out.println("Sorted with Comparable Interface on Title");
        Arrays.sort(myBooks); // uses the Comparable compareTo in the bean
        displayBooks(myBooks);

        System.out.println("Sorted with Comparable Object on Pages");
        Arrays.sort(myBooks, bookPageComparator); // uses the Comparator object
        displayBooks(myBooks);

        System.out.println("Sorted with Comparable lambda expression on Publishers");
        Arrays.sort(myBooks, (s1, s2) -> {
            return s1.getPublisher().compareTo(s2.getPublisher());
        }); // uses the Comparator lambda
        displayBooks(myBooks);

        System.out.println("Sorted with Comparable lambda function on ISBN");
        Arrays.sort(myBooks, comparing(Book::getIsbn)); // Comparable function
        displayBooks(myBooks);
    }

    /**
     * Print the contents of each Book object in the array
     *
     * @param theBooks
     */
    private void displayBooks(Book[] theBooks) {
        for (Book b : theBooks) {
            System.out.print(b.getIsbn() + "\t");
            System.out.print(b.getTitle() + "\t");
            System.out.print(b.getAuthor() + "\t");
            System.out.print(b.getPublisher() + "\t");
            System.out.println(b.getPages());
        }
        System.out.println();
    }

    /**
     * Where it all begins
     *
     * @param args
     */
    public static void main(String[] args) {
        BeanTester bt = new BeanTester();
        bt.perform();
        System.exit(0);
    }
}

Value returned by Comparable
Xenon compared to Boron: 22

Value returned by Comparator
99 compared to 108: -9

Unsorted
200XenonHamiltonHarcourt99
500BoronBradburyPrentice108
300RadonHeinleinThompson98
404ArgonCampbellHachette102

Sorted with Comparable Interface on Title
404ArgonCampbellHachette102
500BoronBradburyPrentice108
300RadonHeinleinThompson98
200XenonHamiltonHarcourt99

Sorted with Comparable Object on Pages
300RadonHeinleinThompson98
200XenonHamiltonHarcourt99
404ArgonCampbellHachette102
500BoronBradburyPrentice108

Sorted with Comparable lambda expression on Publishers
404ArgonCampbellHachette102
200XenonHamiltonHarcourt99
500BoronBradburyPrentice108
300RadonHeinleinThompson98

Sorted with Comparable lambda functions based on ISBN
200XenonHamiltonHarcourt99
300RadonHeinleinThompson98
404ArgonCampbellHachette102
500BoronBradburyPrentice108