Create method absoluteAdd

Create a method that takes 2 integers, and returns the sum of the absolute value of both integers.

System.out.println(absoluteAdd(-5, -7)); // 12
System.out.println(absoluteAdd(6, -2)); // 8
System.out.println(absoluteAdd(-3, 1)); // 4
System.out.println(absoluteAdd(9, 4)); // 13

Create method countingByOne

Create a method that takes 2 integers, print out the numbers from the first number to the second number changing by a count of 1.
- Don’t worry about how the output looks. As long as the numbers are printed in the right order.

countingByOne(10, 5); // 10, 9, 8, 7, 6, 5
countingByOne(12, 19); // 12, 13, 14, 15, 16, 17, 18, 19
countingByOne(1, 1); // 1

Debugging Practice

The code below is broken. I have placed the expected output in the comments. Using the debugger tool and everything you’ve learned about loops, go through and debug this faulty code so it prints as expected.

import java.util.*;

public class DebuggingPractice {
    public static void main(String[] arg) {
        Scanner sc = new Scanner(System.in);
        
        /**
           Expected output:
           
           How many layers in your pyramid do you want?
           4

           *
           * *
           * * *
           * * * *
         */
        System.out.println("How many layers in your pyramid do you want?");
        int levels = sc.nextInt();
        
        System.out.println();
        
        for (int i=0; i<=levels; i++) {
            for (int j=i-1; j>0; j++) {
                System.out.print("* ");
            }

            System.out.println();
        }

        /**
           Expected output:
           
           What is your name?
           Turk

           K R U T
         */
        System.out.println("What is your name?");
        String str = sc.nextLine().toUpperCase();
        String str2 = "";

        System.out.println();
        for (int i=str.length(); i<0; i--) {
            str2 += str.charAt(i);
        }

        System.out.println(str2);

        sc.close();
    }
}

if/else if/else <-> switch/case

Create a method that repeatedly asks the user for an integer, then output the day of the week that number is. 0 is Sunday, 1 is Monday, 2 is Tuesday, etc. End when the user inputs an invalid day of the week.
- Write 2 methods, one using if/else if/else statements, and another using switch/case statements.

Enter a day of the week (0 - 6): 3
3 is Wednesday
Enter a day of the week (0 - 6): 6
6 is Saturday
Enter a day of the week (0 - 6): 15
15 is an invalid day of the week

Trace nested if/else if/else statements

What will get printed onto the console? No IDE!

public class NestedMysteryCode {
    public static void main(String[] args) {
        nestedMysteryCode(5, 10, 3);
        nestedMysteryCode(7, 2, 7);
        nestedMysteryCode(4, 4, 4);
    }

    public static void nestedMysteryCode(int a, int b, int c) {
        if (a > b) {
            if (b < c) {
                System.out.println("Case 1");
            } else {
                System.out.println("Case 2");
            }
        } else if (a < b) {
            if (b > c) {
                if (c != 0) {
                    System.out.println("Case 3");
                } else {
                    System.out.println("Case 4");
                }
            } else if (b == c) {
                if (a >= 0) {
                    System.out.println("Case 5");
                } else {
                    System.out.println("Case 6");
                }
            } else {
                System.out.println("Case 7");
            }
        } else {
            if (b == c) {
                System.out.println("Case 8");
            } else if (b > c) {
                if (a % 2 == 0) {
                    System.out.println("Case 9");
                } else {
                    System.out.println("Case 10");
                }
            } else {
                if (c > 0) {
                    System.out.println("Case 11");
                } else {
                    System.out.println("Case 12");
                }
            }
        }
    }
}

while <-> do-while <-> for

Create a method that repeatedly asks the user for an integer until either 10 numbers are entered or a negative number is entered. Sum up all the numbers entered by the user, excluding the negative number.
- Write 3 versions, using a different type of loop each time.
  - Loops: While | Do-While | For

Enter a number: 6
Enter a number: 9
Enter a number: 1
Enter a number: 5
Enter a number: 3
Enter a number: 7
Enter a number: 6
Enter a number: 8
Enter a number: 4
Enter a number: 3
Sum of all the numbers you entered is 52

Enter a number: 3
Enter a number: 4
Enter a number: 9
Enter a number: 1
Enter a number: -2
Sum of all the numbers before the negative number is 17

Array Declaration 2D

Problem 1: Create a method that takes a 2D array of characters, and prints them out in a grid pattern.
- Output must match the sample output (spaces between each symbol and a new line for each row)
Problem 2: What type and what method did I use to create the symbols2D array?
- Ragged/Jagged Array with Shorthand Notation
- Ragged/Jagged Array with Multi-Step Approach
- Standard Array with Shorthand Notation
- Standard Array with Multi-Step Approach

char[][] symbols2D = {
    {'!', '@', '#'},
    {'$', '%', '^'},
    {'&', '*', '(', ')'}
}

! @ #
$ % ^
& * ( )

Array Declaration 3D

Problem 1: Create a method that takes a 3D array of characters and print them out as followed.
- Output must match the sample output (headers for each row, a tab (\t), then the symbols)
- Hint:
  - Row is the first [2]
  - Each row in the row is the [3]
    - Hence 3 rows
  - The number of symbols per row of each row is the last [2]
Problem 2: What type and what method did I use to create the symbols3D array?
- Ragged/Jagged Array with Shorthand Notation
- Ragged/Jagged Array with Multi-Step Approach
- Standard Array with Shorthand Notation
- Standard Array with Multi-Step Approach

char[][][] symbols3D = new char[2][3][2];
symbols3D[0][0][0] = '!';
symbols3D[0][0][1] = '@';
symbols3D[0][1][0] = '#';
symbols3D[0][1][1] = '$';
symbols3D[0][2][0] = '%';
symbols3D[0][2][1] = '^';
symbols3D[1][0][0] = '&';
symbols3D[1][0][1] = '*';
symbols3D[1][1][0] = '(';
symbols3D[1][1][1] = ')';
symbols3D[1][2][0] = '-';
symbols3D[1][2][1] = '=';

Row 1:
    ! @
    # $
    % ^
Row 2:
    & *
    ( )
    - =

Random number generation + Search for value

Problem 1: Create a method that takes in an integer and generates an integer array of that size, filled with random numbers from 1 to 100 (inclusive)

import java.util.Arrays

System.out.println(Arrays.toString(generateArray1to100(8)));
System.out.println(Arrays.toString(generateArray1to100(5)));
System.out.println(Arrays.toString(generateArray1to100(12)));

Problem 2: Using the array of random numbers generator from Problem 1, print out the smallest even and odd number, and the largest even and odd number.
- This problem may be a bit tricky. It is different from a standard find the smallest/largest problem. But a hint that may help is that the array from problem 1 is always numbers from 1 to 100.
- Think about edge cases! How should your code behave when there are no odd/even numbers?

int[] array = generateArray1to100(20);
System.out.println(Arrays.toString(array));
minMaxOddEven(array);

Sample Outputs

minEven: 8
maxEven: 96
minOdd: 13
maxOdd: 95

It is possible to not have even/odd numbers and for the min/max to be the same number!

minEven: None
maxEven: None
minOdd: 52
maxOdd: 52

Array Search 2D

Problem 1: Create a method that takes in a string array. Then print out all words that are of length 6 or more.

String[] words = {
    "apple", "banana", "cherry", "dog", "elephant", "fish",
    "grape", "hat", "igloo", "jacket", "kangaroo",
    "lemon", "monkey", "noodle", "orange", "penguin",
    "quilt", "rabbit", "snake", "tiger", "umbrella",
    "vanilla", "watermelon", "xylophone", "yogurt", "zebra",
    "sun", "moon", "star", "flower", "ocean", "mountain",
    "river", "cloud", "rain", "snow", "fire", "earth",
    "wind", "volcano", "island", "desert", "forest",
    "castle", "dragon", "knight", "princess", "wizard",
    "unicorn"
};

Problem 2: Create a method that takes in a 2D string array. Then print out all words that are of length 6 or more.

String[][] words2D = {
    {"apple", "banana", "cherry"},
    {"dog"},
    {"elephant", "fish", "grape", "hat"},
    {"igloo", "jacket", "kangaroo"},
    {"lemon", "monkey"},
    {"noodle"},
    {"orange", "penguin", "quilt", "rabbit", "snake"},
    {"tiger", "umbrella", "vanilla", "watermelon", "xylophone"},
    {"yogurt", "zebra"},
    {"sun", "moon", "star", "flower"},
    {"ocean"},
    {"mountain", "river", "cloud", "rain"},
    {"snow"},
    {"fire", "earth", "wind", "volcano", "island"},
    {"desert", "forest", "castle", "dragon", "knight"},
    {"princess", "wizard"},
    {"unicorn"}
};

Expected Out For Both Problems

banana
cherry
elephant
igloo
jacket
kangaroo
monkey
noodle
orange
penguin
rabbit
umbrella
vanilla
watermelon
xylophone
yogurtflower
mountain
volcano
island
desert
forestcastle
dragon
knight
princesswizard
unicorn

Managing and manipulating array contents

Problem 1: Create a method that takes in an array and squares each element in the array.
Problem 2: Create a method that takes the array from Problem 1, and calculate the average.

import java.util.Arrays;

// Problem 1 Test Case
int[] array = {7, 1, 4, 9, 18, 72, 36, 65};
squareUp(array);
System.out.println(Arrays.toString(array)); // [49, 1, 16, 81, 324, 5184, 1296, 4225]

// Problem 2 Test Case
System.out.println(average(array)); // 1397

Generate Random Numbers

Create a method that generates a random String of length 6, using only 0-9 and a-f, then add 0x in front of it. Also generate a random number from 1 to 16777215.
- Please use the given main method and do not make any modifications to it.
- Fun fact: 0xfa12ce is what we call a hexadecimal number.

public static void main(String[] args) {
    Object[] numbers = generateRandomNumbers();
    String hex = (String) numbers[0];
    int dec = (int) numbers[1];
    System.out.printf("Random Hexadecimal Number: %s%n", hex);
    System.out.printf("Random Decimal Number: %d%n", dec);
}

Tracing Method Calls

What is the output of this code?

import java.util.Arrays;
public class Main {
    public static int firstMethod(int[] arr, int x) {
        int z = 0;
        for (int i = 0; i < arr.length; i++) {
            z = z + arr[i] * x;
        }
        return z;
    }

    public static String secondMethod(int x, String str) {
        String s = "";
        for (int i = 0; i < x; i++) {
            s = s + str;
        }
        return s;
    }

    public static double[] thirdMethod(int x) {
        double[] arr = new double[x];
        for (int i = 0; i < x; i++) {
            arr[i] = x;
        }
        return arr;
    }

    public static void finalMethod(int x, String str, double[] arr) {
        System.out.printf("%d     %s     %s", x, str, Arrays.toString(arr));
    }

    public static void main(String[] args) {
        finalMethod(firstMethod(new int[]{5, 7, 35, 52}, 3), secondMethod(3, "xyz"), thirdMethod(5));
    }
}

Complete The Coin Machine

Complete the coin machine class.
- Output does not need to match.
- The amount the coins add up to much be correct.
- The output format must be kept.
  - Please use the given method changeGiven

public class Main {
    public static void main(String[] args) {
        CoinMachine cm = new CoinMachine(50, 50, 50, 50);

        cm.giveChange(50.00, 49.99);
        cm.giveChange(35.00, 27.99);
        cm.giveChange(32.00, 25.00);
        cm.giveChange(1.23, 0.95);
        cm.giveChange(0.75, 0.55);
        cm.giveChange(33.33, 27.75);
        cm.giveChange(0.92, 0.50);
        cm.inStorage();
    }
}

public class CoinMachine {
    private int quarter;
    private int dime;
    private int nickel;
    private int penny;

    public CoinMachine() {
        this.quarter = 0;
        this.dime = 0;
        this.nickel = 0;
        this.penny = 0;
    }

    public CoinMachine(int quarter, int dime, int nickel, int penny) {
        this.quarter = quarter;
        this.dime = dime;
        this.nickel = nickel;
        this.penny = penny;
    }

    public void giveChange(double payment, double price) {
        if (payment < price) {
            System.out.println("Customer did not pay enough.");
            return;
        }

        // keep count of amount of each coin that is going to be given to the user
        int q = 0;
        int d = 0;
        int n = 0;
        int p = 0;

        // payment - how much the user pays
        // price   - their total for the purchase
        /**********************************************/
        // TODO: calculate the amount of coins needed 

        /**********************************************/
    }

    private void changeGiven(int quarter, int dime, int nickel, int penny) {
        System.out.println("Coins used:");
        System.out.printf("%d Quarter(s)%n", quarter);
        System.out.printf("%d Dime(s)%n", dime);
        System.out.printf("%d Nickel(s)%n", nickel);
        System.out.printf("%d Penny(s)%n", penny);
    }

    public void inStorage() {
        System.out.printf("%-10s%d%n", "25¢", this.quarter);
        System.out.printf("%-10s%d%n", "10¢", this.dime);
        System.out.printf("%-10s%d%n", "5¢", this.nickel);
        System.out.printf("%-10s%d%n", "1¢", this.penny);
    }

    public void addQuarter(int count) {
        if (count < 0) {
            System.out.println("Negative not allowed.");
        } else {
            this.quarter = this.quarter + count;
        }
    }

    public void addDime(int count) {
        if (count < 0) {
            System.out.println("Negative not allowed.");
        } else {
            this.dime = this.dime + count;
        }
    }

    public void addNickel(int count) {
        if (count < 0) {
            System.out.println("Negative not allowed.");
        } else {
            this.nickel = this.nickel + count;
        }
    }

    public void addPenny(int count) {
        if (count < 0) {
            System.out.println("Negative not allowed.");
        } else {
            this.penny = this.penny + count;
        }
    }
}

Sample Expected Output

Coins used:
Quarter(s)
Dime(s)
Nickel(s)
Penny(s)
Coins used:
Quarter(s)
Dime(s)
Nickel(s)
Penny(s)
Coins used:
Quarter(s)
Dime(s)
Nickel(s)
Penny(s)
Coins used:
Quarter(s)
Dime(s)
Nickel(s)
Penny(s)
Coins used:
Quarter(s)
Dime(s)
Nickel(s)
Penny(s)
Coins used:
Quarter(s)
Dime(s)
Nickel(s)
Penny(s)
Coins used:
Quarter(s)
Dime(s)
Nickel(s)
Penny(s)
25¢       0
10¢       0
5¢        0
1¢        0

HAS-A

Figure out the output of this code without the use of an IDE.

public class Main {
    public static void main(String[] args) {
        A a = new A(17);
        B b = a.riddle();
        b.answer();
    }
}

class A {
    private B b;
    private int c;

    public A() {
    }

    public A(int c) {
        this.b = new B(c);
        this.c = c * 2;
    }

    public B riddle() {
        System.out.println("My number is twice that of the other number.");
        System.out.println("Added together, our sum is " + (this.c + this.b.getC()) + ".");
        System.out.println("What are our numbers?");
        return this.b;
    }
}

class B {
    private int c;
    
    public B() {
    }

    public B(int c) {
        this.c = c;
    }
    
    public int getC() {
        return this.c;
    }

    public void answer() {
        System.out.println("Our numbers are " + this.c + " and " + this.c * 2 + ".");
    }
}

IS-A

Figure out the output of this code without the use of an IDE.

public class Main {
    public static void main(String[] args) {
        A a = new A();
        B b = new B();
        A ab = new B();
        B ba = (B) ab;

        a.one();
        a.two();
        b.one();
        b.two();
        ab.one();
        ab.two();
        ba.one();
        ba.two();
    }
}

class A {
    public A() {
    }

    public void one() {
        System.out.println("I am a statement.");
    }

    public void two() {
        System.out.println("I am another statement.");
    }
}

class B extends A {
    public B() {
    }

    @Override
    public void one() {
        System.out.println("I am one more statement.");
    }
}

(Trick or Treat) and Trace!

Figure out the output of this code without the use of an IDE.

public class Main {
    public static void main(String[] args) {
        Halloween you = new Halloween();
        you.buyCandy(50);
        for (int i = 1; i <= 5; i++) {
            you.giveCandy(i * ((i % 2 == 0) ? 3 : 4));
        }
        System.out.printf("I end the night with %d piece(s) of candy.%n", you.getCandy());
    }
}

public class Halloween {
    private int candy;

    public Halloween() {
        this.candy = 0;
    }

    public Halloween(int candy) {
        this.candy = candy;
    }

    public int getCandy() {
        return this.candy;
    }

    public int buyCandy(int amount) {
        if (amount < 0) {
            System.out.println("Silly you, you can't buy negative pieces of candy :)");
        } else {
            System.out.printf("You went out and bought %d piece(s) of candy.%n", amount);
            this.candy = this.candy + amount;
        }

        return this.candy;
    }

    public int giveCandy(int amount) {
        if (amount < 0) {
            System.out.println("Silly you, you can't give negative pieces of candy :)");
        } else {
            System.out.printf("You gave out %d piece(s) of candy.%n", amount);
            this.candy = this.candy - amount;
        }

        return this.candy;
    }

    public void trickOrTreat(boolean treat) {
        if (treat) {
            System.out.printf("Here are %d pieces of candy!%n", 5);

        } else {
            System.out.printf("You have been tricked and had %d pieces of candy stolen from you :(%n", 2);
        }
    }
}