Java if-else statements help the program execute the blocks of code only if the specified test condition evaluates to either true or false.
The if-else statement in Java is the most basic of all the flow control statements. An if-else statement tells the program to execute a certain block only if a particular test evaluates to true , else execute the alternate block if the condition is false.
The if and else are reserved keywords in Java, and cannot be used as other identifiers.
A simple if-else statement is written as follows. It starts with a mandatory if statement, followed by an optional else part.
if (condition) < //statement-1 >else < //statement-2 >The condition must be a boolean expression and must evaluate to either true or false . If the condition evaluates to true, statement-1 is executed. Otherwise, statement-2 is executed.
Note that the else block is optional. We may write a statement as :
if (condition) < //statement-1 >2. The If-else Example
Let’s see an example of an if-else statement. In the following program, we check whether the employee’s age is greater than 18. On both bases, we print that the employee is a minor or an adult.
int age = employee.getAge(); if(age > 18) < System.out.println("Employee is adult"); >else
3. Nested If-else Statements
The if-else statements can be nested as well. The inner if-else statements will be executed based on the evaluation results of the outer conditional statements.
In the following program, we are using else-if statement to add an additional conditional that will be evaluated only when the first condition in if block is evaluated as false.
int age = employee.getAge(); if(age > 60) < System.out.println("Employee is retired"); >else if(age > 18) < //Executes only when if condition is false i.e. age is less than 60 System.out.println("Employee is adult"); >else
4. Use Curly Braces to Group Multiple Statements
Consider the following program:
int num1, num2, num3 = 10; if (num1 > 40) num2 = num2 + 10; num3 = num3 + 10; else num2 = num2 - 10; num3 = num3 - 10;The above program will not compile. What’s wrong with the above program? The answer is that we can place only one statement between if and else, in any if-else statement without using the curly braces.
In case of multiple statements, we must bundle the statements into one block statement using curly braces, like so:
if (num1 > 40) < num2 = num2 + 10; num3 = num3 + 10; >else
5. Using Ternary Operator to Replace Simple if-else
We can also use the ternary operator instead of a simple if-else statement to make the code more concise and readable.
Consider a simple if-else statement that checks if a number is greater than or less than a value, and stores the value in a variable.
boolean isAdult; if (age > 18) < isAdult = true; >else
We can write similar instructions using the ternary operator as follows. Look how clean it is.
boolean isAdult = age > 18 ? true : false;