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Control statements are the
statements which alter the flow of execution and provide better control to the
programmer on the flow of execution. In Java control statements are categorized
into selection control statements, iteration control statements and jump
control statements.
· Java’s Selection Statements: Java
supports two selection statements: if and switch. These statements allow us to
control the flow of program execution based on condition.
o if
Statement: if statement performs a task depending on whether a condition is
true or false.
Syntax: if
(condition)
statement1; else
statement2;
Here, each statement may be a single statement or a
compound statement enclosed in curly braces (that is, a block). The condition
is any expression that returns a boolean value. The else clause is optional.
Program 1: Write a program to find biggest of three numbers.
//Biggest of three numbers class BiggestNo
{
public static void main(String args[])
{
int a=5,b=7,c=6;
if ( a> b && a>c)
System.out.println ("a is big");
else if ( b > c)
System.out.println ("b is big");
else
System.out.println ("c is big");
}
}
o Switch Statement: When there are several options and we have to choose only one option from the available ones, we can use switch statement.
Syntax: switch (expression)
{ case value1: //statement sequence
break;
case value2: //statement sequence
break;
………….…..
case valueN: //statement sequence break;
default: //default statement sequence
}
Here, depending on the value of the expression, a particular corresponding case will be executed.
Program 2: Write a program for using the switch statement to execute a particular task depending on color value.
//To display a color name depending on color value class ColorDemo
{ public static void main(String args[])
{ char color = ‘r’; switch (color)
{ case ‘r’: System.out.println (“red”); break; case ‘g’: System.out.println (“green”); break; case ‘b’: System.out.println (“blue”); break; case ‘y’: System.out.println (“yellow”); break; case ‘w’: System.out.println (“white”); break;
default: System.out.println (“No Color Selected”);
}
}
}
o while Loop: while loop repeats a group of statements as long as condition is true. Once the condition is false, the loop is terminated. In while loop, the condition is tested first; if it is true, then only the statements are executed. while loop is called as entry control loop.
Syntax: while (condition)
{
statements;
}
Program 3: Write a program to generate numbers from 1 to 20.
//Program to generate numbers from 1 to 20. class Natural
{ public static void main(String args[])
{ int i=1; while (i <= 20)
{ System.out.print (i + “\t”);
i++;
}
}
}
do…while loop is also called as exit control loop.
Syntax: do
{
statements;
} while (condition);
Program 4: Write a program to generate numbers from 1 to 20.
//Program to generate numbers from 1 to 20. class Natural
{ public static void main(String args[])
{ int i=1;
do
{ System.out.print (i + “\t”);
i++;
} while (i <= 20);
}
}
o for Loop: The for loop is also same as
do…while or while loop, but it is more compact syntactically. The for loop executes a group of statements
as long as a condition is true.
Syntax: for
(expression1; expression2; expression3)
{
statements;
}
Here, expression1 is used to initialize the variables, expression2 is
used for condition checking and expression3 is used for increment or decrement
variable value.
· Java’s
Jump Statements: Java supports three jump statements: break, continue and
return. These statements transfer control to another part of the program.
o break:
Ø break
can be used inside a loop to come out of it.
Ø break
can be used inside the switch block to come out of the switch block.
Ø break
can be used in nested blocks to go to the end of a block. Nested blocks
represent a block written within another block.
Syntax: break; (or)
break
label;//here label represents the name of the block.
o continue: This statement is useful to
continue the next repetition of a loop/ iteration. When continue is executed,
subsequent statements inside the loop are not executed.
Syntax: continue;
Program 7: Write a program to generate numbers from 1 to 20.
//Program
to generate numbers from 1 to 20. class Natural
{ public static void main (String args[])
{
int i=1;
while
(true)
{
System.out.print (i + “\t”);
i++;
if
(i <= 20 )
continue; else break;
}
}
}
o return statement:
Ø
return statement in main method terminates the
application.
Ø
return statement can be used to return some
value from a method to a calling method.
Syntax:
return; (or)
\
Program
8: Write a program to demonstrate return statement.
//Demonstrate
return class
ReturnDemo
{ public
static void main(String args[])
{
boolean t = true;
System.out.println
(“Before the return”);
if
(t)
return;
System.out.println
(“This won’t execute”);
}
Note:
goto statement is not available in java, because it leads to confusion
and forms infinite loops.