class Book {
    String title;
    String author;
    int numPages;
    boolean isCopyrighted;
    
    Book( String _title, String _author, int _numPages, boolean _isCopyrighted ) {
        this.title = _title;
        this.author = _author;
        this.numPages = _numPages;
        this.isCopyrighted = _isCopyrighted;
        }

    /* ( Template for book-handling functions: )
      
       ... funcForBook( /* Book this * / ) {
          ... this.title
          ... this.author
          ... this.numPages
          ... this.isCopyrighted
          }
    */
    
  
    /** @return The amount of time it takes the average reader to read a book (in minutes) */
    double readingTime( /* Book this */ ) {
        return 2 * this.numPages;
        }
    
    @Override
    public String toString( /* Book this */ ) {
        return this.title
             + ", by "
             + this.author
             + " (" + this.numPages + "pp)"
             + (this.isCopyrighted  ?  " ©"  :  "" );
        }

    /** @return a book just like `a-book`, but with bigger text (hence, more pages). */
    Book enbiggen( /* Book this */ ) {
        return new Book( this.title,
                         this.author,
                         2*this.numPages,
                         this.isCopyrighted );
        }

    /** @return a brand new book, based on an original.
     *  The result's authoor will be the original author & the `newAuthor`,
     *  and the result has `numNewPages` pages added to the original.
     */
    Book deriveFrom( /* Book this */ String newAuthor, int numNewPages  ) {
        return new Book( "Son of " + this.title,
                         this.author + " & " + newAuthor,
                         this.numPages + numNewPages,
                         false );
        }

    
    
    /* All code has to be inside a method in Java, so we'll stick our unit-tests in here. */ 
    static void test() {
        Book b0, b1;
        b1 = new Book( "The Cat in the Hat", "Seuss", 37, true );
        b0 = new Book( "The Soul of Wit", "Barland", 0, false );
        
        
        assert (new Book( "The Cat in the Hat", "Seuss", 37, true )).readingTime() == 74.0;
        assert b0.readingTime() == 0;
        
        
        assert b1.enbiggen().equals(new Book( "The Cat in the Hat", "Seuss", 74, true ));
        assert (new Book( "The Bat in the Mat", "Streuss", 1, true )).enbiggen()
               .equals(new Book( "The Bat in the Mat", "Streuss", 2, true ));
        assert b0.enbiggen().equals(b0);
        
        assert b1.deriveFrom("Barland", 10)
                 .equals( new Book( "Son of The Cat in the Hat"
                                  , "Seuss & Barland"
                                  , 47
                                  , false ) );
        
        assert b0.deriveFrom("Banksie", 99)
                 .equals( new Book( "Son of The Soul of Wit"
                                  , "Barland & Banksie"
                                  , 99
                                  , false ) );
        
        assert b0.equals(b0);
        assert !b0.equals(b1);
        assert b1.equals( new Book( "The Cat in the Hat", "Seuss", 37, true ) );
        assert b0.hashCode() == b0.hashCode();
        assert b1.hashCode() == new Book( "The Cat in the Hat", "Seuss", 37, true ).hashCode();
        assert b1.toStringDebug().equals( "new Book( \"The Cat in the Hat\", \"Seuss\", 37, true )" );
        }

    /** Just run our unit tests. Be sure to run `java` with `--assertionsEnabled` (or, `-ea`). */
    public static void main( String[] __ ) {
        test();
        // Alternately, we could just stick the tests directly into `main` here, that's fine too.
        }
    
    // OOPS -- this does not override Object#equals(Object)
    public boolean equals( /* Book this, */ Book that ) {
        return this.title.equals( that.title )
            && this.numPages == that.numPages;
    }
    @Override
    public boolean equals( /* Book this, */ @Nullable Object that ) {
        if (that==null) {
            return false;
            }
        else if (this==that) {
            return true;
            }
        else if (this.getClass() != that.getClass()) {
            // Many say to use `instanceof` ^^here^^; I disagree. --ibarland
            return false;
            }
        else {
            Book thatt = (Book)that;
            return this.author.equals(thatt.author)
                && this.title.equals(thatt.title)
                && this.numPages == thatt.numPages
                && this.isCopyrighted == thatt.isCopyrighted;
            }
        }
    
    
    
    // as a Java/O.O. programmer, memorize:
    // NEVER OVERRIDE EQUALS WITHOUT OVERRIDING HASHCODE
    // (Built-in libraries -- especially Collections -- rely on the
    // property that if a.hashCode()!=b.hashCode(), then !a.equals(b)
    // and so they won't actually call `equals` if the hashcodes differ.
    // ...Java's default hashCode, like default `equals`/`==`/`toString`
    // returns the memory address.
    // (So the default equals + hashCode DOES have the desired property, happily;
    //  it's up to you to remember to [repeat with me] Never override
    //  `equals` without also overriding `hashCode`.)
    
    private static Integer theHash = null;
    private static int SHUFFLE_BITS = 0b11111; //31;
    
    @Override
    public int hashCode( /* Book this */ ) {
        if (theHash == null) {
            // We only reach this once per object.
            // (relies on immutability).
            int h = 0;
            h += title.hashCode();
            h *= SHUFFLE_BITS;
            h += author.hashCode();
            h *= SHUFFLE_BITS;
            h += (new Integer(numPages)).hashCode();
            h *= SHUFFLE_BITS;
            h += (new Boolean(isCopyrighted)).hashCode();
            theHash = new Integer(h);
            }
        return theHash.intValue();
        }
    
    /** @return a string suitable for a programmer to read.
     *   It can be copied/pasted into Java source code.
     */
    public String toStringDebug( /* Book this */ ) {
        String separator = ", ";
        return "new Book( "
             + "\"" + this.title  + "\"" + separator
             + "\"" + this.author + "\"" + separator
             + this.numPages + separator
             + this.isCopyrighted
             + " )";
        }
    
    
    }