Java Branching: If, Else, Elif

This page is a continuation to the explanation of control flow. If and else statements let your program conditionally execute particular blocks of code.

If Statement

The Java if statement is used to conditionally run code depending on if a boolean condition is true. It checks a boolean condition: true or false. There are various types of if statement in Java.

A condition in the context of control flow statements refers to any boolean expression (previously explained here) that evaluates to either true or false. Some examples include 2 > 3, x == 9, 6 % 2 == 0, and x == 9 && y == 3

Consider the following structure of an if statement:

if (condition) {
    // Here we put whatever code we want to run if the condition is true
}

If you need a refresher on boolean expressions, refer to here

Here are some examples of if statements:

int x = 3;
if (x > 9) { // This code will not be executed since x is equal to 3 and 3 is less than 9 
    System.out.println("X is bigger than 9!");
}

Here’s an example that includes the use of operator shorthand to subtract y by 2:

int y = 9;
y-=2;
if (y < 8) { // This code will be executed because y = 9, 9 - 2 = 7 and 7 is less than 8.
    System.out.println("Y is smaller than 8!");
}

Here’s an example using the or operator:

int x = 1;
int y = 3;
if (x < 2 || y > 20) { // This code will be executed as even though y is not greater than 20, x is less than 2.
    System.out.println(" :) ");
}

Else

The else statement is used in conjunction with the if statement to run code only if the above if statement is not run. Consider the following example:

int x = 1;
if (x > 3) {
    System.out.println("X is greater than 3!");
} else {
    System.out.println("X is less than 3 :(");
}

In the above example, “X is greater than 3!” will be printed to the screen if the condition inside the if statement is true. In this instance however x is less than 3, which means that the else statement is run instead, printing out “X is less than 3 :(” to the console.

We can also think of an if-else chain as testing the condition inside the if statement, running the code inside the if statement if it’s true, or running the code inside the else statement if false.

You can only have one else statement for each for loop.

Else if

While there can only ever be one else statement in Java, we can use else if statements. These can be chained together and together, and with this chaining, we can test multiple different statements, and not just only two. The last tested thing can be an else statement, after an else statement there can be no other else ifs or elses

int x = 7;

if (x > 10) {
    System.out.println("X is greater than 10!");
} 
else if (x > 5) {
    System.out.println("X is greater than 5 but less than or equal to 10!");
} 
else if (x > 5) {
   System.out.println("X is 5 or less.");
}
else {
    ...
}

In a chain of if/ else statements, even if multiple conditions are true, only the top most truthful block will be executed, and the others are discarded. If there are multiple if statements without the else keyword, then each statement will be checked, regardless if the one above was true or false.

Resources

W3Schools Java Conditionals