Loops and conditions are the building blocks of Java programs. This chapter will help us understand the important loops and conditions through examples. Learning these loops and conditions in Java will make writing code easier.
Let's see how the for loop works. The for loop is one of the most commonly used loops in Java programs, and it it is very important to understand how it works internally. So, let's say we want to print the numbers from 1 to 100 using the forloop. For the syntax to execute the numbers from 1 to 100 in a sequence and to write that in a for loop, we will simply write:
// 1 to 100
/* for(initialization;condition;increment)
{
} */
for (int i=0;i<100;i++)
{
system.out.println(i);
}
}
Since we want to print 0, 1, 2, 3, we use i++. This means for every loop, it increments only by 1. And while looping, each time, it also checks whether the preceding condition is satisfied. So, if 1 is less than 100, it goes inside; if 2 is less than 100, it goes inside. Until this condition is satisfied, it will keep on looping. When the value of i reaches 100, 100 is less than 100, which is false. At that time, it terminates the loop and comes out of it. We will use a basic example here:
for (int i=0;i<5;i++)
{
system.out.println(i);
}
To run test cases in debug mode in the IDE, double-click at the location shown in the following screenshot:
Line from which the debugging begins
When you see the blue icon, run that in the debug mode by clicking the insects-like symbol. It will ask you to launch in debug mode. Just click on Save to do so:
Debug icon at the top of the editor
You will see all the variable values here. Step by step, we'll go inside the loop, and will execute the next step of the program:
Variable value while debugging
Finally, when it reaches the value 4, and is incremented by 1 again, it is 5. Note that it comes out of the loop without going inside that after the value becomes 5. So, that means the condition is no longer satisfied and the loop will run five times. The output is shown in the following screenshot:
Final output as per the code
So, that's how the for loop works.
Now, if we set the condition to the following, it will not go inside the for loop, even for the first time since, the condition is false.:
for (int i=5;i<3;i++)
On running the preceding condition in in the debug mode, the complete loop is skipped,and nothing is seen in the output.
Let's see another example:
for (int i=0;i<10;i+2 )
The output will be:
0
2
4
6
8
This is how the for loop works internally.
In the next section, we will learn about the if...else and do...while loops.
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Before we learn the while and do...while loops, we will discuss the if condition in this section. In a Java program, when the if conditional statement is used, the statement in the if block is executed only if the condition is satisfied. Otherwise the statement from else block is run. Also this execution is just takes place once. In a for loop, a variable is initiated and the loop runs till the condition is satisfied.
However, in the if case, it will not keep on looping. It will just go inside the loop once the if condition is satisfied; otherwise, it will go into the else block. So, control will execute the statements present in this else block, as shown in the following screenshot:
Output of the if...else condition as per the code
But all this happens only once, unlike the for loop, where a condition is satisfied until it goes back and executes.
Let's take a look at the following example:
if(5>2)
{
System.out.println("success");
}
else
{
System.out.println("fail");
}
The following screenshot displays those errors:
Quick fixes drop down with suggestions to correct the code error
The first error is to remove the including condition, which can be ignored. On running the preceding program, you will see the output as success because the condition 5 greater than 2 that went inside is true:
Output displays success as per the code
If we change the condition and make 5 less than 2, making the condition false, it will skip to the else block and execute the statement present in else.
code to receive fail as the output
This time the output should be fail, as shown in the following screenshot:
Output displays success as per the code
This is how the if condition works.
Note...
