Decision Making in Java

What is Decision making?

In programming, the sequential execution of statements may not always be sufficient. There are situations where we need to execute certain statements based on specific conditions or repeat a group of statements until certain conditions are met. In such cases, we use decision-making constructs like conditionals (e.g., if-else statements) and loops.

When it comes to loops, their purpose typically revolves around the decision of whether to repeat the loop or not. Loops allow us to execute a block of code repeatedly until a certain condition is satisfied. This condition determines whether the loop should continue iterating or terminate.

Decision Making with if Statement

The if statement can be implemented in different forms listed below:

1. Simple if statement

2. if.. else statement

3. Nested if...else statement

4. else if ladder

1. Simple if Statement

The "if" statement in programming is a fundamental decision-making construct used to control the flow of execution based on a certain condition. It allows a program to choose between two different paths of execution depending on whether the condition evaluates to true or false.

Fig 1. Flowchart for simple if statement

The syntax of the "if" statement in Java is as follows:

if (condition) {
      // code to be executed if the condition is true
}

The keyword "if" is followed by a condition enclosed in parentheses.

The condition is evaluated, resulting in a boolean value (true or false).

If the condition evaluates to true, the block of code within the curly braces immediately following the "if" statement is executed.

2. if.. else statement

The "if" statement in programming is a fundamental decision-making construct used to control the flow of execution based on a certain condition. It allows a program to choose between two different paths of execution depending on whether the condition evaluates to true or false.

Fig 2. Flowchart for if... else statement

The syntax of the "if... else" statement in Java is as follows:

if (test_expression) {
    // Statements to execute if the test_expression is true
} else {
    // Statements to execute if the test_expression is false
}

how it works:

The keyword "if" is followed by a test expression enclosed in parentheses.

The test expression is evaluated, resulting in a boolean value (true or false).

If the test expression evaluates to true, the block of code within the curly braces immediately following the "if" statement is executed.

If the test expression evaluates to false, the block of code within the curly braces following the "else" keyword is executed.

The "else" block is optional. If omitted, the program continues execution after the "if" block if the test expression is false.

By utilizing "if" statements, programmers can implement branching logic in their programs, enabling them to execute different sets of instructions based on varying conditions. This allows for more dynamic and responsive behavior in software applications.

3. Nested if...else statement

Nested if-else statements in Java allow for more complex decision-making scenarios where you have multiple levels of conditions to check. This means having an "if" statement (or a series of "if" statements) inside another "if" or "else" block.

Fig 3. Flowchart for nested if... else statement

The basic syntax of a nested if-else statement in Java looks like this:

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

how it works:

The outer "if" statement checks the first condition (condition1).

If condition1 is true, the code block inside the outer "if" statement is executed.

Within this block, there's another "if" statement (the nested "if").

The nested "if" statement checks the second condition (condition2).

If both condition1 and condition2 are true, the code block inside the nested "if" statement is executed.

If condition1 is true but condition2 is false, the "else" block of the nested "if" statement is executed.

If condition1 is false, the code block inside the outer "else" block is executed.

Nested if-else statements are useful when you need to perform different checks or actions based on multiple conditions, and the outcome depends on the combination of those conditions.

Here's an example to illustrate a nested if-else statement:

int x = 10;
int y = 5;

if (x > 5) {
    if (y > 3) {
        System.out.println("Both x and y are greater than their respective thresholds.");
    } else {
        System.out.println("x is greater than 5, but y is not greater than 3.");
    }
} else {
    System.out.println("x is not greater than 5.");
}

In this example, the output will be "Both x and y are greater than their respective thresholds." if both x and y satisfy their respective conditions. Otherwise, it will print the corresponding messages based on the conditions evaluated.

Check your knowledge:

1. What is the primary purpose of decision-making constructs in programming?

A) To execute statements sequentially

B) To control the flow of execution based on specific conditions

C) To define loops for repetitive tasks

D) To organize code into functions

2. Which of the following statements describes the functionality of an "if" statement?

A) It executes a block of code repeatedly until a condition is met.

B) It chooses between two different paths of execution based on a condition.

C) It defines a loop for iterating over a collection of elements.

D) It performs mathematical calculations within a program.

3. In Java, what is the syntax of a simple "if" statement?

A) if (condition) { // code }

B) if { condition } [ code ]

C) condition { if code }

D) code { if condition }

4. What happens if the condition in an "if" statement evaluates to false?

A) The program continues with the next statement after the "if" block.

B) The program terminates immediately.

C) The code inside the "else" block is executed.

D) An error is thrown by the compiler.

5. Which statement correctly describes a nested if-else statement?

A) It consists of multiple if statements placed one after the other.

B) It allows for multiple conditions to be checked independently.

C) It involves an "if" statement inside another "if" or "else" block.

D) It executes a block of code repeatedly based on a condition.

6. What is the purpose of a nested if-else statement?

A) To execute a block of code repeatedly.

B) To define loops for repetitive tasks.

C) To perform complex decision-making based on multiple conditions.

D) To print messages to the console.

7. What is the syntax of a nested if-else statement in Java?

A) if { condition } [ code ] else { code }

B) if (condition) { code } else { code }

C) if (condition1) { if (condition2) { code } else { code } } else { code }

D) if (condition1) { code1 } else { if (condition2) { code2 } }

8. In a nested if-else statement, where is the code executed if condition1 is false?

A) Inside the outer "if" block

B) Inside the outer "else" block

C) Inside the nested "if" block

D) Nowhere, the program terminates

Answers:

1. B) To control the flow of execution based on specific conditions

2. B) It chooses between two different paths of execution based on a condition.

3. A) if (condition) { // code }

4. C) The code inside the "else" block is executed.

5. C) It involves an "if" statement inside another "if" or "else" block.

6. C) To perform complex decision-making based on multiple conditions.

7. C) if (condition1) { if (condition2) { code } else { code } } else { code }

8. B) Inside the outer "else" block