b). do -while loop:-
If we want to execute loop body at-least once then we should go for the do-while loop.
Syntax:-
do
{
body
} while (b);
where ; the semicolon is mandatory and b always should be a boolean type.
1. The arguments should be a boolean type . If we are trying to provide any other type then we will get compile time error.
example:
int b=10;
do
{
body
} while (b);
Compile Time Error: Incompatible Type
Found:int
Required:boolean
2.Curly braces{ } are optional and without Curly braces { } we can take one statement under
while which should not be the declarative statement.
Example:-
do
System.out.println("Hello");
while(true);
valid
Example:-
do;
while(true); valid (semicolon is valid java statement)
Example:-
do invalid
while(true);
Example:-
do
int x=10; invalid
while(true);
Example:-
do
{
int x=10; valid
} while(true);
Important Loop Holes in do-while loop
1.Take a look at the following expression which looks like an invalid but they are perfectly valid.
example:-
do while(true)
System.out.println("JavaByChetan");
while(false);
In the above expression, it looks like while the argument is false so no output will be produced but it is not correct .
In do-while execution if flow from do to while that 's why this statement will be executed and we will get the output:
JavaByChetan
JavaByChetan
infinite times...
This Expression will be Executed like this:
do
while(true)
System.out.println("JavaByChetan");
while(false);
2.Unreachable Statement
example 1:-
do
{
System.out.println("Hello");
}while(true);
System.out.println("Hii"); Compile Time Error: Unreachable state
example 2:-
do
{
System.out.println("Hello");
}while(false);
System.out.println("Hii"); output: Hello
Hii
example 3:-
int a=10,b=20;
do
{
System.out.println("Hello");
}while(a<b);
int a=10,b=20;
do
{
System.out.println("Hello");
}while(a<b);
System.out.println("Hii"); output: Hello
Hello.....infinite times
example 4:-
int a=10,b=20;
do
{
System.out.println("Hello");
}while(a>b);
int a=10,b=20;
do
{
System.out.println("Hello");
}while(a>b);
System.out.println("Hii"); output: Hello
Hii
example 5:-
final int a=10,int b=20;
do
{
System.out.println("Hello");
}while(a<b);
final int a=10,int b=20;
do
{
System.out.println("Hello");
}while(a<b);
System.out.println("Hii"); Compile Time Error: Unreachable state
example 6:-
final int a=10,int b=20;
do
{
System.out.println("Hello");
}while(a>b);
final int a=10,int b=20;
do
{
System.out.println("Hello");
}while(a>b);
System.out.println("Hii"); output: Hello
Hii
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