Chapter 03 - SELECTIONS

Introduction:

Java provides selection statements where you can select various courses of action.

For example:

            if (radium < 0) {
              System.out.println("Incorrect input");
            }
            else {
              area = radius * radius * 3.14159
              System.out.println("Area is " + area);
            }
          

Boolean Data Types:

Selection statements use conditions that are Boolean expressions, ie. true or false. Boolean declares data type variable with the value either true or false.

There are six relational operators:

• "<" less than
• "<=" less than or equal to
• ">" greater than
• ">=" greater than or equal to
• "==" equal to
• "!=" not equal to

Boolean variable holds boolean value which is either true or false (true and false are also reserved words). Here is an example.

      import java.util.Scanner;

        public class AdditionQuiz {
        public static void main(String[] args) {
          int number1 = (int)(System.currentTimeMillis() % 10);
          int number2 = (int)(System.currentTimeMillis() / 10 % 10);

          // Create a Scanner
          Scanner input = new Scanner(System.in);

          System.out.print(
          "What is " + number1 + " + " + number2 + "? ");

          int answer = input.nextInt();

          System.out.println(
          number1 + " + " + number2 + " = " + answer + " is " +
          (number1 + number2 == answer));
            }
          }
      

Check Point Questions:

3.1 List six relational operators:

1. >= is the greater than or equal to sign
2. <= is the less than or equal to sign
3. < is the less than sign
4. > is the greater than sign
5. == is the equal to sign
6. #= is the not equal to sign

3.2 Assuming that x is 1, show the result of the following Boolean expressions:

• (x > 0) is true
• (x < 0) is false
• (x != 0) is true
• (x >= 0) is false
• (x != 1) is false

3.3 Can the following conversions involving casting be allowed? Write a test program to verify your answer

           boolean b = true;
           i = (int)b;
           int i = 1;
           boolean b = (boolean)i;
         

if statemements:

Java has several selection statements:

1. one-way if statement - excutes an action only if condition is true. Does not do anything if the condition is false.
2. two-way if statement - excutes an action if the condition is true. And performs another action if the condition is false.
3. nested if statement
4. multi-way if statement
5. switch statement
6. conditional expressions

The following statement:

          if (i > 0) {
            System.out.printlin("i is positive");
          }
        

is the same as (the brace has been omitted):

          if (i > 0)
            System.out.printlin("i is positive");
        

Check Point Questions:

3.4 Write an if statement that assigns 1 to x if y is greater than 0.

        import java.util.Scanner;

        public class Assign1toX {

          public static void main(String[] args) {

              int x = 0;

              Scanner input = new Scanner(System.in);
              System.out.print("Enter a y value");
              int y = input.nextInt();

              if (y > 0) {
                  x += 1;
                  System.out.println("x is " + x);

          }

        }
        }
      

3.5 Write an if statement that increases pay by 3% if score is > 90.

      import java.util.Scanner;

      /*
      *
      * @author Haresh Vaswani
      * @date 10/16/2021
      */

      public class IncreasePayby3 {

      public static void main(String[] args) {

        double pay = 1000;

        Scanner input = new Scanner(System.in);
        System.out.print("Enter score: ");
        int score = input.nextInt();

        if (score > 90) {
            pay *= 1.03;
            System.out.println("pay increased by " + pay);

          }

        }

      }
    

Two-way if-else Statements:

Two-way if-else statements performs a function when the condition is false. Unlike the one-way if statement which performs function when the statement is true.

    import java.util.Scanner;

    /*
    *
    * @author Haresh Vaswani
    * @date 10/16/2021
    */

    public class IncreasePayby3 {

      public static void main(String[] args) {

        double pay = 1000;

        Scanner input = new Scanner(System.in);
        System.out.print("Enter score: ");
        int score = input.nextInt();

        if (score > 90) {
            pay *= 1.03;
            System.out.println("pay increased by " + pay);
      }
        else {
            pay *= 1.01;
            System.out.println("pay increased by " + pay);
        }

      }

    }
  

Saddleback College Lecture on Chapter 3