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Challenges

Remember the rules for this are

  • Try to use only the information given up to this point in this book.
  • Try not to give up until you've given it a solid attempt

Challenge 1

What will this program output when run? Write down your guess and then try running it.

~IF toplevel_anonymous_class

void main() {
    String first = "1";
    String second = "2";
    String result = first + second;

    System.out.println(result);
}

~ELSE

public class Main {
    public static void main(String[] args) {
        String first = "1";
        String second = "2";
        String result = first + second;

        System.out.println(result);
    }
}

~ENDIF

Challenge 2

What will this program output when run? Write down your guess and then try running it.

~IF toplevel_anonymous_class

void main() {
    String first = "1";
    int second = 2;

    System.out.println(first + second);
}

~ELSE

public class Main {
    public static void main(String[] args) {
        String first = "1";
        int second = 2;

        System.out.println(first + second);
    }
}

~ENDIF

Challenge 3

What will this program output when run? Write down your guess and then try running it.

~IF toplevel_anonymous_class

void main() {
    char first = 'a';
    String second = "b";
    String third = "ab";

    System.out.println((first + second).equals(second));
}

~ELSE

public class Main {
    public static void main(String[] args) {
        char first = 'a';
        String second = "b";
        String third = "ab";

        System.out.println((first + second).equals(second));
    }
}

~ENDIF

Challenge 4

Make it so this program will output abc by only changing one line and not altering the println statement.

Before your change, why does it output 294?

~IF toplevel_anonymous_class

void main() {
    char a = 'a';
    char b = 'b';
    char c = 'c';
    System.out.println(a + b + c);
}

~ELSE

public class Main {
    public static void main(String[] args) {
        char a = 'a';
        char b = 'b';
        char c = 'c';
        // Change above this line
        System.out.println(a + b + c);
    }
}

~ENDIF

Challenge 5

Without adding any new printlns, change one line in this program so that it outputs racecar.

Try to find two ways to do that.

~IF toplevel_anonymous_class

void main() {
    String racecar = "racecar";

    int diff = 1;

    int index = 6;

    System.out.print(racecar.charAt(index));
    index += diff;
    System.out.print(racecar.charAt(index));
    index += diff;
    System.out.print(racecar.charAt(index));
    index += diff;
    System.out.print(racecar.charAt(index));
    index += diff;
    System.out.print(racecar.charAt(index));
    index += diff;
    System.out.print(racecar.charAt(index));
    index += diff;
    System.out.println(racecar.charAt(index));
}

~ELSE

public class Main {
    public static void main(String[] args) {
        String racecar = "racecar";

        int diff = 1;

        int index = 6;

        System.out.print(racecar.charAt(index));
        index += diff;
        System.out.print(racecar.charAt(index));
        index += diff;
        System.out.print(racecar.charAt(index));
        index += diff;
        System.out.print(racecar.charAt(index));
        index += diff;
        System.out.print(racecar.charAt(index));
        index += diff;
        System.out.print(racecar.charAt(index));
        index += diff;
        System.out.println(racecar.charAt(index));
    }
}

~ENDIF