Conditionals in Java: If, Else, and Switch - datacouch-io/spark-java GitHub Wiki

Understanding Java Conditional Statements

Java includes the standard logical conditions inspired by mathematics:

• Less than: a < b
• Less than or equal to: a <= b
• Greater than: a > b
• Greater than or equal to: a >= b
• Equal to: a == b
• Not Equal to: a != b

These conditions allow you to execute different actions based on specific decisions.

In Java, you can work with the following conditional statements:

1. if Statement: Use if to specify a block of code to execute if a given condition is true.
2. else Statement: Use else to specify a block of code to execute if the same condition is false.
3. else if Statement: Use else if to define a new condition to test if the initial condition is false.
4. switch Statement: Employ switch to define multiple alternative blocks of code to execute.

Note: In Java, if is case-sensitive, so it must be written in lowercase. Uppercase letters (e.g., If or IF) will result in an error.

Syntax for if, else if, and else Statements:

if (condition1) {
  // Code block to execute if condition1 is true
} else if (condition2) {
  // Code block to execute if condition1 is false and condition2 is true
} else {
  // Code block to execute if both condition1 and condition2 are false
}

Here's an example:

int time = 22;

if (time < 10) {
  System.out.println("Good morning.");
} else if (time < 20) {
  System.out.println("Good day.");
} else {
  System.out.println("Good evening.");
}
// Outputs "Good evening."

Shortened Syntax for Ternary Conditionals:

When you have only one statement to execute for if and else, you can use a shortened form called the ternary conditional:

variable = (condition) ? expressionTrue : expressionFalse;

Example:

int time = 20;
String result = (time < 18) ? "Good day." : "Good evening.";
System.out.println(result);

Java Switch Statements

The switch statement allows you to choose one of several code blocks to execute based on the value of an expression.

Syntax for switch Statement:

switch (expression) {
  case x:
    // Code block to execute if expression matches x
    break;
  case y:
    // Code block to execute if expression matches y
    break;
  default:
    // Code block to execute if expression matches none of the cases
}

Here's how it works:

• The switch expression is evaluated once.
• The expression's value is compared with the values of each case.
• If a match is found, the corresponding code block is executed.
• The optional break keyword is used to exit the switch block, preventing further code execution and case testing.

Here's an example that uses the day of the week number to determine the weekday name:

int day = 4;
switch (day) {
  case 1:
    System.out.println("Monday");
    break;
  case 2:
    System.out.println("Tuesday");
    break;
  case 3:
    System.out.println("Wednesday");
    break;
  case 4:
    System.out.println("Thursday");
    break;
  case 5:
    System.out.println("Friday");
    break;
  case 6:
    System.out.println("Saturday");
    break;
  case 7:
    System.out.println("Sunday");
    break;
}
// Outputs "Thursday" (day 4)

These conditional statements in Java allow you to control the flow of your programs based on various conditions and inputs.