Java if, if…else Statement
Updated Jan 6, 2021 View by 1.8 K
In this article, you will learn to use two selection statements: if and if…else to control the flow of your program’s execution.
In programming, it’s often desirable to execute a certain section of code based upon whether the specified condition is true or false (which is known only during the run time). For such cases, control flow statements are used.
Java if (if-then) Statement
The syntax of if-then statement in Java is:
if (expression) {
// statements
}
Here expression is a boolean expression (returns either true or false).
If the expression is evaluated to true, statement(s) inside the body of if (statements inside parenthesis) are executed.
If the expression is evaluated to false, statement(s) inside the body of if are skipped from execution.
How if statement works?
Example 1: Java if Statement
class IfStatement {
public static void main(String[] args) {
int number = 10;
if (number > 0) {
System.out.println("Number is positive.");
}
System.out.println("This statement is always executed.");
}
}
When you run the program, the output will be:
Number is positive. This statement is always executed.
When number is 10, the test expression number > 0 is evaluated to true. Hence, codes inside the body of if statements are executed.
Now, change the value of number to a negative integer. Let’s say -5. The output in this case will be:
This statement is always executed.
When number is -5, the test expression number > 0 is evaluated to false. Hence, Java compiler skips the execution of body of if statement.
To learn more about test expression and how it is evaluated, visit relational and logical operators.
Java if…else (if-then-else) Statement
The if statement executes a certain section of code if the test expression is evaluated to true. The if statement may have an optional else block. Statements inside the body of else statement are executed if the test expression is evaluated to false.
The syntax of if-then-else statement is:
if (expression) {
// codes
}
else {
// some other code
}
How if…else statement works?
Example 2: Java if else Statement
class IfElse {
public static void main(String[] args) {
int number = 10;
if (number > 0) {
System.out.println("Number is positive.");
}
else {
System.out.println("Number is not positive.");
}
System.out.println("This statement is always executed.");
}
}
When you run the program, the output will be:
Number is positive. This statement is always executed.
When number is 10, the test expression number > 0 is evaluated to true. In this case, codes inside the body of if are executed, and codes inside the body of else statements are skipped from execution.
Now, change the value of number to a negative number. Let’s say -5. The output in this case will be:
Number is not positive. This statement is always executed.
When number is -5, the test expression number > 0 is evaluated to false. In this case, codes inside the body of else are executed, and codes inside the body of if statements are skipped from execution.
Java if..else..if Statement
In Java, it’s possible to execute one block of code among many. For that, you can use if..else…if ladder.
if (expression1)
{
// codes
}
else if(expression2)
{
// codes
}
else if (expression3)
{
// codes
}
.
.
else
{
// codes
}
The if statements are executed from the top towards the bottom. As soon as the test expression is true, codes inside the body of that if statement is executed. Then, the control of program jumps outside if-else-if ladder.
If all test expressions are false, codes inside the body of else is executed.
Example 3: Java if..else..if Statement
class Ladder {
public static void main(String[] args) {
int number = 0;
if (number > 0) {
System.out.println("Number is positive.");
}
else if (number < 0) {
System.out.println("Number is negative.");
}
else {
System.out.println("Number is 0.");
}
}
}
When you run the program, the output will be:
Number is 0.
When number is 0, both test expression number > 0 and number < 0 is evaluated to false. Hence, the statement inside the body of else is executed.
The above program checks whether number is positive, negative or 0.
Java Nested if..else Statement
It’s possible to have if..else statements inside a if..else statement in Java. It’s called nested if...else statement.
Here’s a program to find largest of 3 numbers:
Example 4: Nested if…else Statement
class Number {
public static void main(String[] args) {
Double n1 = -1.0, n2 = 4.5, n3 = -5.3, largestNumber;
if (n1 >= n2) {
if (n1 >= n3) {
largestNumber = n1;
} else {
largestNumber = n3;
}
} else {
if (n2 >= n3) {
largestNumber = n2;
} else {
largestNumber = n3;
}
}
System.out.println("Largest number is " + largestNumber);
}
}
When you run the program, the output will be:
Largest number is 4.5
Note: In above programs, we have assigned value of variables ourselves to make this easier. However, in real world applications, these values may come from user input data, log files, form submission etc.
You should also check ternary operator in Java, which is kind of shorthand notation of if...else statement.
