If Statements in Java

While writing code in any language, you will have to control the flow of your program - you will want to execute a certain piece of code if a condition is satisfied, and some different code in case it is not.

If statements are used to make these decisions in code. The keyword if tells Java to execute the code in the curly braces under certain conditions, defined in the parentheses. These conditions are known as boolean conditions and they may only be true or false.

When the condition evaluates to true, the program executes the statement inside the curly braces. When the boolean condition evaluates to false, the statement inside the curly braces will not execute. But what will happen then?

Normally nothing would happen. But with an else statement, an alternate block of code can be executed.

if (test expression) {
    // run code if test expression is true
}
else {
    // run code if test expression is false
}

When writing if statements, we usually compare two values using one or more comparison operators:

Operator	Name	Examples
==	Equal	x == 5, x == y
!=	Not equal	x != 3, x != y
>	Greater than	x > 5, x > y
<	Less than	x < 8, x < y
>=	Greater than or equal to	x >= 4, x >= y
<=	Less than or equal to	x <= 3, x <= y

We can also combine multiple conditional statements with the help of logical operators:

Operator	Name	Description	Examples
&&	And	Returns true if both statements are true	x < 5 && x < 10
\|\|	Or	Returns true if one of the statements is true	x < 5 \|\| x < 10
!	Not	Reverses the result, returns false if the result is true	!(x < 5 && x < 10)

Let's go through some examples together to better understand how if-else statements work:

# Declare 2 variables and initialize them
int a = 2;
int b = 3;

// Prints "a equals 2"
if(a == 2) {
  System.out.println("a equals 2");
}

// Prints nothing
if(b != 3) {
  System.out.println("b is not equal to 3");
}

// Prints "b equals 3"
if(a == 2 && b - a == 1) {
  System.out.println("b is equal to 3");
}

// Prints "a = 2, b = 3"
if(a != 2 || b != 3) {
  System.out.println("Inside if");
}
else {
  System.out.println("a = 2, b = 3");
}

// Prints "a + b equals 5"
if(!(a + b == 5)) {
  System.out.println("a + b is not equal to 5");
}
else {
  System.out.println("a + b equals 5");
}

// Prints "a is even, b is odd"
if(a % 2 == 0) {
  if(b % 2 == 0) {
    System.out.println("Both a and b are even");
  }
  else {
    System.out.println("a is even, b is odd");
  }
}
else {
  if(b % 2 == 0) {
    System.out.println("a is odd, b is even");
  }
  else {
    System.out.println("Both a and b are odd");
  }
}

Assignment
Follow the Coding Tutorial and let's write some if-else statements.

Hint
Look at the examples above if you get stuck.

Introduction

In this lesson, we will explore the concept of if statements in Java. These statements are fundamental for controlling the flow of a program based on certain conditions. Understanding how to use if statements effectively is crucial for making decisions in your code, which is a common requirement in many programming scenarios.

Common scenarios where if statements are particularly useful include validating user input, controlling the flow of a game, and handling different cases in business logic.

Understanding the Basics

The if statement in Java allows you to execute a block of code only if a specified condition is true. This condition is a boolean expression, meaning it evaluates to either true or false. If the condition is true, the code inside the if block runs; otherwise, it is skipped.

Here is a simple example:

int number = 10;
if (number > 5) {
    System.out.println("The number is greater than 5");
}

In this example, the condition number > 5 evaluates to true, so the message "The number is greater than 5" is printed.

Main Concepts

Let's delve deeper into the key concepts and techniques involved in using if statements:

Comparison Operators: These operators are used to compare two values. Common comparison operators include == (equal to), != (not equal to), > (greater than), < (less than), >= (greater than or equal to), and <= (less than or equal to).
Logical Operators: These operators are used to combine multiple boolean expressions. Common logical operators include && (and), || (or), and ! (not).
Else Statement: The else statement allows you to specify an alternate block of code to run if the condition in the if statement is false.

Here is an example that combines these concepts:

int age = 20;
if (age >= 18) {
    System.out.println("You are an adult.");
} else {
    System.out.println("You are a minor.");
}

In this example, the condition age >= 18 evaluates to true, so the message "You are an adult." is printed. If the condition were false, the message "You are a minor." would be printed instead.

Examples and Use Cases

Let's look at some more examples to see how if statements can be used in various contexts:

int score = 85;
if (score >= 90) {
    System.out.println("Grade: A");
} else if (score >= 80) {
    System.out.println("Grade: B");
} else if (score >= 70) {
    System.out.println("Grade: C");
} else if (score >= 60) {
    System.out.println("Grade: D");
} else {
    System.out.println("Grade: F");
}

In this example, the program assigns a grade based on the value of score. This demonstrates how multiple if and else if statements can be used to handle different cases.

Common Pitfalls and Best Practices

When using if statements, it's important to be aware of common mistakes and follow best practices:

Avoid Deep Nesting: Deeply nested if statements can make your code hard to read and maintain. Consider using logical operators or breaking the code into smaller functions.
Use Braces: Always use curly braces {} even for single-line statements. This improves readability and reduces the risk of errors.
Optimize Conditions: Combine conditions using logical operators to make your code more concise and efficient.

Advanced Techniques

Once you are comfortable with basic if statements, you can explore more advanced techniques:

Switch Statements: For multiple conditions based on the same variable, consider using a switch statement for better readability and performance.
Ternary Operator: The ternary operator ?: provides a shorthand way to write simple if-else statements.

Here is an example of the ternary operator:

int number = 10;
String result = (number % 2 == 0) ? "Even" : "Odd";
System.out.println(result);

In this example, the ternary operator checks if number is even or odd and assigns the appropriate string to result.

Code Implementation

Let's implement a more comprehensive example that demonstrates the use of if statements:

public class IfStatementExample {
    public static void main(String[] args) {
        int temperature = 25;

        // Check if temperature is above 30
        if (temperature > 30) {
            System.out.println("It's hot outside.");
        } else if (temperature >= 20 && temperature <= 30) {
            System.out.println("The weather is nice.");
        } else {
            System.out.println("It's cold outside.");
        }

        // Check if temperature is exactly 25
        if (temperature == 25) {
            System.out.println("The temperature is exactly 25 degrees.");
        }
    }
}

In this example, we check the value of temperature and print different messages based on its value. This demonstrates how to use multiple if and else if statements to handle different conditions.

Debugging and Testing

When working with if statements, debugging and testing are crucial to ensure your code works as expected:

Use Print Statements: Add print statements inside your if blocks to check which conditions are being met.
Write Test Cases: Create test cases to cover different scenarios and edge cases. This helps ensure your code handles all possible inputs correctly.

Here is an example of a simple test case:

public class IfStatementTest {
    public static void main(String[] args) {
        testTemperature(35); // Expected output: "It's hot outside."
        testTemperature(25); // Expected output: "The weather is nice." and "The temperature is exactly 25 degrees."
        testTemperature(15); // Expected output: "It's cold outside."
    }

    public static void testTemperature(int temperature) {
        if (temperature > 30) {
            System.out.println("It's hot outside.");
        } else if (temperature >= 20 && temperature <= 30) {
            System.out.println("The weather is nice.");
        } else {
            System.out.println("It's cold outside.");
        }

        if (temperature == 25) {
            System.out.println("The temperature is exactly 25 degrees.");
        }
    }
}

Thinking and Problem-Solving Tips

When approaching problems that require if statements, consider the following strategies:

Break Down the Problem: Divide the problem into smaller parts and handle each condition separately.
Use Flowcharts: Create flowcharts to visualize the decision-making process and ensure all conditions are covered.
Practice: Solve coding exercises and projects that involve if statements to improve your problem-solving skills.

Conclusion

In this lesson, we covered the basics of if statements in Java, including comparison and logical operators, the else statement, and advanced techniques like the ternary operator. We also discussed common pitfalls, best practices, and provided examples to illustrate these concepts.

Mastering if statements is essential for controlling the flow of your programs and making decisions based on conditions. Practice writing if statements in different scenarios to become more proficient in using them.

Additional Resources

For further reading and practice, consider the following resources: