Java/com/study/demo3/Book.java

package com.study.demo3;

public class Book {
  protected String isbn;
  protected String title;
  protected boolean available;

  public Book() {
    this.available = true;
  }

  public Book(String isbn, String title) {
    this.isbn = isbn;
    this.title = title;
    this.available = true;
  }

  public Book(String isbn, String title, boolean available) {
    this.isbn = isbn;
    this.title = title;
    this.available = available;
  }

  public String getIsbn() {
    return isbn;
  }

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

  public String getTitle() {
    return title;
  }

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

  public boolean isAvailable() {
    return available;
  }

  public void setAvailable(boolean available) {
    this.available = available;
  }

  public void returnBook() {
    if (!this.available) {
      this.available = true;
      System.out.println(
          this.title + " (ISBN: " + this.isbn + ") has been returned and is now available.");
    } else {
      System.out.println(this.title + " (ISBN: " + this.isbn + ") is already available.");
    }
  }
}