Tutorial 22: Loops in Java

Loops in Java : Loops are useful when you have to execute the same lines of code repeatedly, for a specific number of times or as long as a specific condition is true. Suppose you want to type a ‘Hello’ message 100 times in your Output. Of course, you will have to copy and paste the same line 100 times. Instead, if you use loops, you can complete this task in just 3 or 4 lines.
There are three types of loops in Java.
for loop
while loop
do-while loop
A for loop statement contains the initialization, condition and increment/decrement in one line thereby providing a shorter, easy to debug structure of looping.
Syntax :
for(initialization ;condition ; incr / decr)
{
//statement or code to be executed
}
It consists of four parts:
Initialization: It is the initial condition which is executed once when the loop starts. Here, we can initialize the variable, or we can use an already initialized variable. It is an optional condition.
Condition: It is the second condition which is executed each time to test the condition of the loop. It continues execution until the condition is false.
Statement: The statement of the loop is executed each time until the second condition is false.
Increment/Decrement: It increments or decrements the variable value. It is an optional condition.
The Java while loop is used to iterate a part of the program several times. If the number of iteration is not fixed, it is recommended to use while loop.
Syntax :
while (condition){
//code to be executed
}
While loop starts with the checking of condition. If it evaluated to true, then the loop body statements are executed otherwise first statement following the loop is executed. For this reason it is also called Entry control loop
Once the condition is evaluated to true, the statements in the loop body are executed. Normally the statements contain an update value for the variable being processed for the next iteration.
When the condition becomes false, the loop terminates which marks the end of its life cycle.
do while loop is similar to while loop with only difference that it checks for condition after executing the statements, and therefore is an example of Exit Control Loop.
Syntax :
do{
Statements
}
while (condition);
do while loop starts with the execution of the statement(s). There is no checking of any condition for the first time.
After the execution of the statements, and update of the variable value, the condition is checked for true or false value. If it is evaluated to true, next iteration of loop starts.
When the condition becomes false, the loop terminates which marks the end of its life cycle.
It is important to note that the do-while loop will execute its statements atleast once before any condition is checked, and therefore is an example of exit control loop.
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