There are
two types of decision making statements in Java. They are:
· if
statements
· switch
statements
The if Statement:
An if statement consists of a
Boolean expression followed by one or more statements.
Syntax:
The syntax of an if statement is:
if(Boolean_expression)
{
//Statements will execute if the Boolean expression is true
}
If the Boolean expression
evaluates to true then the block of code inside the if statement will be
executed. If not the first set of code after the end of the if statement (after
the closing curly brace) will be executed.
Example:
public class Test {
public static void main(String args[]){
int x = 10;
if( x < 20 ){
System.out.print("This is if statement");
}
}
}
This would produce the following
result:
The if...else
Statement:
An if statement can be followed
by an optional else statement,
which executes when the Boolean expression is false.
Syntax:
The syntax of an if...else is:
if(Boolean_expression){
//Executes when the Boolean expression is true
}else{
//Executes when the Boolean expression is false
}
Example:
public class Test {
public static void main(String args[]){
int x = 30;
if( x < 20 ){
System.out.print("This is if statement");
}else{
System.out.print("This is else statement");
}
}
}
This would produce the following
result:
The if...else if...else
Statement:
An if statement can be followed
by an optional else if...else statement, which is very useful to
test various conditions using single if...else if statement.
When using if , else if , else
statements there are few points to keep in mind.
· An if can
have zero or one else's and it must come after any else if's.
· An if can
have zero to many else if's and they must come before the else.
· Once an
else if succeeds, none of the remaining else if's or else's will be tested.
Syntax:
The syntax of an if...else is:
if(Boolean_expression 1){
//Executes when the Boolean expression 1 is true
}else if(Boolean_expression 2){
//Executes when the Boolean expression 2 is true
}else if(Boolean_expression 3){
//Executes when the Boolean expression 3 is true
}else {
//Executes when the none of the above condition is true.
}
Example:
public class Test {
public static void main(String args[]){
int x = 30;
if( x == 10 ){
System.out.print("Value of X is 10");
}else if( x == 20 ){
System.out.print("Value of X is 20");
}else if( x == 30 ){
System.out.print("Value of X is 30");
}else{
System.out.print("This is else statement");
}
}
}
This would produce the following
result:
Nested if...else
Statement:
It is always legal to nest
if-else statements which means you can use one if or else if statement inside
another if or else if statement.
Syntax:
The syntax for a nested if...else
is as follows:
if(Boolean_expression 1){
//Executes when the Boolean expression 1 is true
if(Boolean_expression 2){
//Executes when the Boolean expression 2 is true
}
}
You can nest else
if...else in the similar way
as we have nested if statement.
Example:
public class Test {
public static void main(String args[]){
int x = 30;
int y = 10;
if( x == 30 ){
if( y == 10 ){
System.out.print("X = 30 and Y = 10");
}
}
}
}
This would produce the following
result:
The switch Statement:
A switch statement allows a variable to be
tested for equality against a list of values. Each value is called a case, and
the variable being switched on is checked for each case.
Syntax:
The syntax of enhanced for loop
is:
switch(expression){
case value :
//Statements
break; //optional
case value :
//Statements
break; //optional
//You can have any number of case statements.
default : //Optional
//Statements
}
The following rules apply to a
switch statement:
· The
variable used in a switch statement can only be a byte, short, int, or char.
· You can
have any number of case statements within a switch. Each case is followed by
the value to be compared to and a colon.
· The value
for a case must be the same data type as the variable in the switch and it must
be a constant or a literal.
· When the
variable being switched on is equal to a case, the statements following that
case will execute until a break statement
is reached.
· When a break statement is reached, the switch
terminates, and the flow of control jumps to the next line following the switch
statement.
· Not every
case needs to contain a break. If no break appears, the flow of control will fall
through to subsequent cases
until a break is reached.
· A switch statement can have an optional default
case, which must appear at the end of the switch. The default case can be used
for performing a task when none of the cases is true. No break is needed in the
default case.
Example:
public class Test {
public static void main(String args[]){
//char grade = args[0].charAt(0);
char grade = 'C';
switch(grade)
{
case 'A' :
System.out.println("Excellent!");
break;
case 'B' :
case 'C' :
System.out.println("Well done");
break;
case 'D' :
System.out.println("You passed");
case 'F' :
System.out.println("Better try again");
break;
default :
System.out.println("Invalid grade");
}
System.out.println("Your grade is " + grade);
}
}
Compile and run above program
using various command line arguments. This would produce the following result:
$ java Test
Well done
Your grade is a C
$
