Lecture 3(1)

Recap From Last Two Lectures

• Designing an APP for ordinary users requested by a bank.

• Important considerations include:

  • Data Types

  • Java Syntax

Motivation

• Example scenario: Assigning a negative value for the radius in ComputeArea.java.

  • Consequence: Program prints an invalid result.

  • Solution: Avoid computation of area if the radius is negative.

boolean Data Type

• Definition: A variable that holds a boolean value is known as a boolean variable.

• Usage: The boolean data type is used for declaring boolean variables.

• Evaluation: A boolean expression evaluates to either true or false.

  • Example: boolean b = (1 > 2); // b is assigned the value false

Comparison in Programs

• In programming, it’s common to compare two values.

• Java provides six comparison (relational) operators:

  • Example Comparisons:

    • i > j

    • radius > 0

Relational Operators in Java

Selection Statements

• Definition: Use conditions that are boolean expressions.

• Types of selection statements in Java:

  • One-way if statements.

  • Two-way if-else statements.

  • Nested if statements.

  • Multi-way if-else statements.

  • Switch statements.

  • Conditional operators.

One-way if Statements

• Structure:

  if (boolean-expression) {
      statement(s);
  }

Example of One-way if Statement

• Code Example:

  if (radius >= 0) {
      area = 3.14 * radius * radius;
      System.out.println("The area for the circle of radius " + radius + " is " + area);
  }

• Note: The boolean expression is enclosed in parentheses, block braces can be omitted for a single statement.

Two-way if-else Statements

• Structure:

  if (boolean-expression) {
      statement(s) for true-case;
  } else {
      statement(s) for false-case;
  }

Example of Two-way if-else Statement

• Code Example:

  if (radius >= 0) {
      area = 3.14159 * radius * radius;
      System.out.println("The area of the circle of radius " + radius + " is " + area);
  } else {
      System.out.println("Negative input");
  }

Classroom Exercise

• Task: Write a program to check if the integer number entered by the user is odd or even.

Random Number Generation

• Syntax: Math.random() produces a random double

• Example: int x = (int) (5 * Math.random()) + 4 generates a random integer in the range [4, 9).

Example: ArithmeticTest

• Write a program to:

  1. Randomly generate two single-digit integers.

  2. Display a question like "What is 3 + 4?".

  3. After the user answers, indicate whether it is correct.

Nested-if Statement

• Definition: An if statement within another if statement.

• Example:

  if (i > k) {
      if (j > k) {
          System.out.println("i and j are greater than k");
      }
  } else {
      System.out.println("i is less than or equal to k");
  }

Sample Program - Grades

• Task: Compute the letter grade based on numeric score (0-100).

  • A: 90-100, B: 80-89, C: 70-79, D: 60-69, F: <60.

Multi-way if-else Statements

• Structure: Check multiple conditions.

  • Example: Trace if-else statements to determine the grade based on a score.

Switch Statements

• Syntax:

  switch (switch-expression) {
      case value1:
          statement(s)1;
          break;
      case value2:
          statement(s)2;
          break;
      default:
          System.out.println("Errors: invalid status");
  }

When to Use Switch vs. If-Else

• Use if-then-else for ranges of values or conditions.

• Use switch for a single integer or enumerated value.

Conditional Operators

• Usage of ternary operator for concise conditions.

  • Example: Instead of using if-else, use: y = (x > 0) ? 1 : -1;.

Logical Operators

• Operators and their meanings:

  • !: NOT

  • &&: AND

  • ||: OR

  • ^: Exclusive OR

Example: Leap Year Calculation

• Write a program to determine if a year is a leap year based on:

  1. Divisible by 400

  2. Or (divisible by 4 AND not divisible by 100).

Practice Exercise 1

• Task: Prompt for IMDB rating and Metascore to determine if a movie is recommended.

  • Criteria: IMDB rating > 7.0 and Metascore > 60.

Practice Exercise 2

• Task: Prompt for year and month to display the number of days in that month.

  • Leap year handling for February.