loops.md

Loops

• Practice writing for-loops and while-loops
• Practice writing a constructor

Prerequisites

• Hello World
• Calculator

Instructions

1. Create a new project called Loops and a new Java class within your project. Name the file Main. Create your main method.

2. Create another Java class within your src folder and name it Loops.

3. Create a method called basicLoops. Write four separate loops that will...

   • Part 1: print variable x in 0-10 inclusive
   • Part 2: print variable x in 0-10 not inclusive of 10
   • Part 3: print variable x in 0-10 inclusive skipping every other number
   • Part 4: print variable x in 10-0 inclusive skipping every other number

4. Create a method called forLoops. Write two separate for loops.

   • Part 1: declare a list called colors of three string elements. Using a for loop, print each element in the list.
   • Part 2: create a new for loop that will iterate through the index and value of each element in colors. In the body of your loop, print the index and value in one line.

5. Create a method called whileLoop. In your method declare an integer variable named x set to 0. Set your loop so that it prints the value of x while x is less than 10. Remember to increase x by 1 in the body of the loop.

6. Create a method called delay. Add two print statements and add code for a 2 second delay between the statements.

7. At the top of your Loops class, add an initializing constructor that prints Initialize

8. Go back to the file with your main method. Inside the main method, create an instance of your Loops class and then call each of the methods from that class. Print the outputs to the console.

Results

Try it yourself before looking at these!

Code

Main.java

        public class Main {
            public static void main(String[] args) throws InterruptedException {
                Loops loopObj = new Loops();
                loopObj.basicForLoops();
                loopObj.forLoops();
                loopObj.whileLoop();
                loopObj.delay();
            }
        
        }

Loops.java

    import java.util.ArrayList;
    import java.util.List;
    
    public class Loops {
    
        public Loops(){
            System.out.println("Initialize");
        }
    
        public void basicForLoops() {
    
            int x = 0;
    
            System.out.print("\nPart 1: ");
            while (x <= 10) {
                System.out.print(x);
                if (x < 10) System.out.print(", ");
                x++;
            }
    
            x = 0;
    
            System.out.print("\nPart 2: ");
            while (x < 10) {
                System.out.print(x);
                if (x < 9) System.out.print(", ");
                x++;
            }
    
            x = 0;
    
            System.out.print("\nPart 3: ");
            while (x <= 10) {
                System.out.print(x);
                if (x < 10) System.out.print(", ");
                x = x + 2;
            }
    
            x = 10;
    
            System.out.print("\nPart 4: ");
            while (x <= 10 && x >= 0) {
                System.out.print(x);
                if (x > 1) System.out.print(", ");
                x = x - 2;
            }
        }
    
        ;
    
        public void forLoops() {
            System.out.println("\nPart 1: ");
            List<String> colors = new ArrayList<String>();
            colors.add("red");
            colors.add("green");
            colors.add("blue");
            for (String color : colors) System.out.println(color);
    
            System.out.println("Part 2: ");
            for (int i = 0; i < colors.size(); i++) System.out.println(i + ": " + colors.get(i));
        }
    
    
        public void whileLoop() {
            int x = 0;
            while (x < 10) {
                System.out.println(x);
                x++;
            }
        }
    
       public void delay() throws InterruptedException {
            System.out.println("FRC5190");
            Thread.sleep(2000);
            System.out.println("Green Hope Falcons");
       }
    
    }

Console Output

basicForLoops

        Initialize
        
        Part 1: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10
        Part 2: 0, 1, 2, 3, 4, 5, 6, 7, 8, 9
        Part 3: 0, 2, 4, 6, 8, 10
        Part 4: 10, 8, 6, 4, 2, 0
        Process finished with exit code 0

forLoops

    Initialize
    
    Part 1: 
    red
    green
    blue
    Part 2: 
    0: red
    1: green
    2: blue

    Process finished with exit code 0

whileLoop

    Initialize
    0
    1
    2
    3
    4
    5
    6
    7
    8
    9
    
    Process finished with exit code 0

delay

    Initialize
    FRC5190
    Green Hope Falcons
    
    Process finished with exit code 0