Decision statements in Java (if-then, if-then-else)
Control flow statements allow us to execute specific code blocks based on a decision. Remember that the general flow of a program is from top to bottom, that is, it is executed from the first line to the last. In this post, we will see how to code the if-then and if-then-else decision statements in Java.
If-Then Statement
This statement allows to execute a code block if the evaluation of a condition results in true. Let's see the following example.
public class Test
{
public static void main(String[] args) {
int number = 10;
if (number > 7) {
System.out.println("The number is greater than 7");
}
}
}
When running this code, we get the following.
The number is greater than 7This means that the evaluation performed resulted in true since 10 > 7.
If-Then-Else Statement
This statement adds an alternative path when the condition is evaluated as false. Let's alter a little bit the previous example and see the following.
public class Test
{
public static void main(String[] args) {
int number = 5;
if (number > 7) {
System.out.println("The number is greater than 7");
} else {
System.out.println("The number is lower than 7");
}
}
}
When running this code, we get the following.
The number is lower than 7This means that the evaluation performed resulted in false since 5 < 7. At this point you might be thinking, what if we have more than two simple conditions?. Let's see the following example reformed from the previous one.
public class Test
{
public static void main(String[] args) {
int number = 7;
if (number > 10) {
System.out.println("The number is greater than 10");
} else if (number > 5) {
System.out.println("The number is greater than 5");
} else {
System.out.println("The number is lower than 5");
}
}
}
When running this code, we get the following.
The number is greater than 5This is because the first condition was false since 7 < 10. Given this, the second condition is evaluated and results in true since 7 > 5. The last block is skipped since the execution entered through one of the preceding conditions.
Complex Conditions
Decision statements can evaluate a decision composed of a complex expression. Let's see the following example.
public class Test
{
public static void main(String[] args) {
int number = 7;
if (number >= 5 && number <= 10) {
System.out.println("The number is between 5 and 10");
} else {
System.out.println("The number is not between 5 and 10");
}
}
}
When running this code, we get the following.
The number is between 5 than 10The && operator indicates that both conditions must be met. Additionally, there are alternative ways to evaluate a condition, such as the ternary operator. Do you remember the first example of the if-then-else statement?. Well, it can also be written in the following way.
public class Test
{
public static void main(String[] args) {
int number = 5;
String comparision = (number > 7) ? "greater" : "lower";
System.out.println("The number is " + comparision + " than 7");
}
}
When running this code, we get the following.
The number is lower than 7It behaves exactly the same as the first example. The difference is that the conditional is executed to assign a String to the variable comparison. In this case, the block that is executed is "lower" and not "greater". When the condition is evaluated as true, the block after the question mark (?) is executed, when it is evaluated as false, the block after the colon ( : ) is executed.