Conditional statements
- The if Statement
Use the if statement to specify a block of Java code to be executed if a condition is true.
Syntax
if (condition) {
// block of code to be executed if the condition is true
}
Note
if is in lowercase letters. Uppercase letters (If or IF) will generate an error.
In the example below, we test two values to find out if 20 is greater than 18. If the condition is true, print some text:
Example
if (20 > 18) {
System.out.println("20 is greater than 18");
}
- The else Statement
Use the else statement to specify a block of code to be executed if the condition is false.
Syntax
if (condition) {
// block of code to be executed if the condition is true
} else {
// block of code to be executed if the condition is false
}
Example 1
int time = 20;
if (time < 18) {
System.out.println("Good day.");
} else {
System.out.println("Good evening.");
}
Output
Good evening
Example 2
int n = 5;
if(n%2==0) {
System.out.println("n is even");
}
else {
System.out.println("n is odd");
}
Output
n is odd
- The else if Statement
Use the else if statement to specify a new condition if the first condition is false.
Syntax
if (condition1) {
// block of code to be executed if condition1 is true
} else if (condition2) {
// block of code to be executed if the condition1 is false and condition2 is true
} else {
// block of code to be executed if the condition1 is false and condition2 is false
}
Example 1
int time = 22;
if (time < 10) {
System.out.println("Good morning.");
} else if (time < 20) {
System.out.println("Good day.");
} else {
System.out.println("Good evening.");
}
Output
Good evening.
Example 2
public class Main{
public static void main(String[] args) {
int a = 10;
int b = 3;
if (a > 5 && b > 5) {
System.out.println(" a>5, b>5");
} else if (a > 5 && b < 5) {
System.out.println(" a>5, b<5");
} else if (a < 5 && b > 5) {
System.out.println(" a<5, b>5");
} else if (a < 5 && b < 5) {
System.out.println(" a<5, b<5");
}
}
}
Output
a>5, b<5
Ternary operator
Syntax:
condition ? true : false
Example:
string result;
result = (6>5) ? "6 is greater than 5" : " 6 is not greater than 5" ;
System.out.println(result);
Output
6 is greater than 5
Nested if Conditions
Syntax:
if(condition1)
{
if(condition2)
{
//Statements
} else
{
//Statements
}
} else
{
// Statements
}
Example
public class Main{
public static void main(String[] args) {
int a = 10;
int b = 3;
if (a > 5) {
if (b > 5) {
System.out.println("a>5 , b>5");
} else {
System.out.println("a>5 , b<5");
}
} else {
if (b > 5) {
System.out.println("a<5 , b>5");
} else {
System.out.println("a<5 , b<5");
}
}
}
}
Output
a>5 , b<5
Switch Statement
The switch statement evaluates an value and matches the value to various cases.
It then executes the code associated with each statement until it encounters a break statement.
Syntax:
switch (expression) {
case value1:
//Statements executed when the
//result of expression matches value1
break;
case value2:
//Statements executed when the
//result of expression matches value2
break;
...
case valueN:
//Statements executed when the
//result of expression matches valueN
break;
default:
//Statements executed when none of
//the values match the value of the expression
break;
}
Example:
int day = 6
switch (day) {
case 0:
day = "Sunday";
break;
case 1:
day = "Monday";
break;
case 2:
day = "Tuesday";
break;
case 3:
day = "Wednesday";
break;
case 4:
day = "Thursday";
break;
case 5:
day = "Friday";
break;
case 6:
day = "Saturday";
break;
default:
day = "Invalid Input";
}
System.out.println(day);
Output
Saturday
Loop Control statements
Loops can execute a block of code as long as a specified condition is reached.
Loops are handy because they save time, reduce errors, and they make code more readable.
While Loop
The while loop loops through a block of code as long as a specified condition is true:
Syntax
while (condition) {
// code block to be executed
}
Example
int i = 0;
while (i < 5) {
System.out.println(i);
i++;
}
Output
0 1 2 3 4
Note:
Do not forget to increase the variable used in the condition, otherwise the loop will never end!
Do/While Loop
The do/while loop is a variant of the while loop. This loop will execute the code block once, before checking if the condition is true, then it will repeat the loop as long as the condition is true.
Syntax
do {
// code block to be executed
}
while (condition);
The loop will always be executed at least once, even if the condition is false, because the code block is executed before the condition is tested:
Example
int i = 10;
do {
System.out.println(i);
i++;
}
while (i < 5);
Output
10
For Loop:
When you know exactly how many times you want to loop through a block of code, use the for loop instead of a while loop:
Syntax
for (statement 1; statement 2; statement 3) {
// code block to be executed
}
Statement 1 is executed (one time) before the execution of the code block.
Statement 2 defines the condition for executing the code block.
Statement 3 is executed (every time) after the code block has been executed.
Example 1
for (int i = 0; i < 5; i++) {
System.out.println(i);
}
Output
0 1 2 3 4
Example2
for (int i = 0; i <= 10; i = i + 2) {
System.out.println(i);
}
Output
0 2 4 6 8 10
Break Statement
The break statement can also be used to jump out of a loop.
This example jumps out of the loop when i is equal to 4:
Example
for (int i = 0; i < 10; i++) {
if (i == 4) {
break;
}
System.out.println(i);
}
Output
0 1 2 3
Continue Example
Example
int i = 0;
while (i < 10) {
if (i == 4) {
i++;
continue;
}
System.out.println(i);
i++;
}
Output
0 1 2 3 5 6 7 8 9