8.2. Types of Statements

Expression Statements:

These statements evaluate expressions and can change the state of the program. Example: Assignment and increment operations:

int a = 5; // Declaration statement
a = a + 1; // Expression statement (assignment)

Expression statements in Java are snippets of code that perform operations on variables, or evaluate expressions. They allow the programmer to modify the state of variables during the program's execution. For example, the statement int a = 5; both declares a variable a and initializes it to 5. The next statement, a = a + 1;, takes the current value of a, adds 1 to it, and stores this new value back in a. This means if a started at 5, after the execution of this expression statement, a would now hold the value of 6.

Think of expression statements like a modified score in a game. Just as you might have a score of 50 points and then score an additional 10 points, changing your total score to 60, expression statements adjust values based on calculations or updates, just like updating your game score.

Control Flow Statements:

These are used to control the execution flow of a program. The most commonly used control flow statements include:

• Conditional Statements (if, else, switch): Control the program flow based on conditions.
• Looping Statements (for, while, do-while): Execute a block of code repeatedly.
• Jump Statements (break, continue): Change the control flow of loops.

Control flow statements dictate how the program behaves in different situations. Conditional statements, like the if statement, allow the program to execute different code blocks based on whether a condition is true or false. For example, if (age >= 18) checks if the age variable is 18 or older; if this is true, the code inside the if block runs, indicating 'Adult'. Looping statements, such as for and while, repeat a block of code multiple times until a condition is met, allowing for iterations without manually writing the code multiple times. Jump statements like break and continue allow altering the flow of loops; break exits the loop, while continue skips to the next iteration.

Imagine you're in a board game where you have to follow certain paths based on the roll of a die. If you roll a higher number, you might move ahead, akin to an 'if' statement determining your next move based on the die's result. If you keep rolling and moving ahead until you reach the end of the board, that's like a loop, repeating until reaching a finish line.

Example of Conditional Statements:

int age = 18;
if (age >= 18) {
    System.out.println("Adult");
} else {
    System.out.println("Minor");
}

Example of Looping Statements:

for (int i = 0; i < 5; i++) {
    System.out.println(i);
}

Example of Switch Statement:

int day = 3;
switch (day) {
case 1:
    System.out.println("Monday");
    break;
case 2:
    System.out.println("Tuesday");
    break;
default:
    System.out.println("Invalid day");
}

These examples illustrate the use of control flow statements in programming. The conditional example checks an age variable to determine if someone is classified as an 'Adult' or 'Minor'. This is a practical way to ensure that age-specific rules are enforced. The looping statement example prints the numbers 0 to 4, demonstrating how a for loop enables the execution of a block of code multiple times without repeating the same lines of code manually. The switch example is used to associate an integer with specific cases, letting the program print different days of the week based on the value of day.

Think of conditional statements like a traffic light. If it's green, you go; if it's red, you stop. Just as drivers must follow these signals based on conditions, your program follows conditional statements that determine what to execute. The for loop is like counting the number of cookies in a jar: you keep going until you reach the end of the jar, just as your loop counts up to a certain number. The switch statement is akin to making a selection from a restaurant menu: depending on what you order (value of day), you receive a different meal (output).

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