In Java, decision-making statements are used to execute a block of code based on certain conditions. These statements control the flow of execution in the program by evaluating boolean expressions (true/false conditions). Java provides several types of decision-making statements:
1. if Statement
- Purpose: Executes a block of code if the condition evaluates to true.
- Syntax:
if (condition) {
// Code to execute if condition is true
}
Example:
public class IfExample {
public static void main(String[] args) {
int number = 10;
if (number > 0) {
System.out.println(“The number is positive.”);
}
}
}
2. if-else Statement
- Purpose: Executes one block of code if the condition is true and another block if it is false.
- Syntax:
if (condition) {
// Code to execute if condition is true
} else {
// Code to execute if condition is false
}
Example:
public class IfElseExample {
public static void main(String[] args) {
int number = -5;
if (number > 0) {
System.out.println(“The number is positive.”);
} else {
System.out.println(“The number is not positive.”);
}
}
}
3. if-else-if Ladder
- Purpose: Used to check multiple conditions sequentially. If one condition is true, the corresponding block of code is executed, and the rest are skipped.
- Syntax:
if (condition1) {
// Code for condition1
} else if (condition2) {
// Code for condition2
} else {
// Code if all conditions are false
}
Example:
public class IfElseIfExample {
public static void main(String[] args) {
int marks = 85;
if (marks >= 90) {
System.out.println(“Grade: A”);
} else if (marks >= 80) {
System.out.println(“Grade: B”);
} else if (marks >= 70) {
System.out.println(“Grade: C”);
} else {
System.out.println(“Grade: F”);
}
}
}
4. switch Statement
- Purpose: Tests a variable for equality against a set of values (cases) and executes the matching block.
- Syntax:
switch (expression) {
case value1:
// Code for case value1
break;
case value2:
// Code for case value2
break;
default:
// Code if no cases match
}
Example:
public class SwitchExample {
public static void main(String[] args) {
int day = 3;
switch (day) {
case 1:
System.out.println(“Monday”);
break;
case 2:
System.out.println(“Tuesday”);
break;
case 3:
System.out.println(“Wednesday”);
break;
default:
System.out.println(“Invalid day”);
}
}
}
Key Points for switch:
- The break statement prevents fall-through to subsequent cases.
- The default case is optional but recommended for unmatched cases.
- From Java 12 onwards, a switch expression is introduced that can return a value.
Switch Expression Example (Java 12+):
public class SwitchExpressionExample {
public static void main(String[] args) {
int day = 3;
String dayName = switch (day) {
case 1 -> “Monday”;
case 2 -> “Tuesday”;
case 3 -> “Wednesday”;
default -> “Invalid day”;
};
System.out.println(“Day: ” + dayName);
}
}
Nested Decision-Making Statements
- Purpose: Decision-making statements can be nested inside other decision-making statements for more complex conditions.
Example:
public class NestedIfExample {
public static void main(String[] args) {
int age = 25;
int weight = 70;
if (age > 18) {
if (weight > 50) {
System.out.println(“Eligible to donate blood.”);
} else {
System.out.println(“Not eligible to donate blood due to weight.”);
}
} else {
System.out.println(“Not eligible to donate blood due to age.”);
}
}
}
Comparison of if and switch
| Feature | if Statement | switch Statement |
| Condition | Evaluates any boolean expression | Works with specific values (int, char, String, enums) |
| Complexity | Suitable for complex conditions | Suitable for simple equality checks |
| Performance | Slower for many conditions | Faster for many discrete cases |
Key Points
- Use if-else:
- When conditions are based on ranges or complex expressions.
- Use switch:
- When comparing a single variable against discrete values.
- Avoid Fall-through in switch:
- Use break statements to prevent unintended execution of subsequent cases.
- Readable Code:
- Ensure decision-making logic is clear and comments explain the conditions.