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In a program, we modify and repeat the data several times. We need some tools for these modifications that will control the flow of the program, and to perform this type of tasks Java Provides control statements.
Java’s Selection statements:
- if
- if-else
- nested-if
- if-else-if
- switch-case
- jump – break, continue, return
The If statement is the most simple decision-making statement. It is used to decide whether a certain statement or block of statements will be executed or not .
i.e if a certain condition is true then a block of statements is executed otherwise not.
if(condition)
{
// Statements to execute if
// condition is true
}Example:
// Java program to illustrate If statement without curly block
import java.util.*;
class IfDemo {
public static void main(String args[])
{
int i = 10;
if (i < 15)
System.out.println("Inside If block"); // part of if block(immediate one statement after if condition)
System.out.println("10 is less than 15"); //always executes as it is outside of if block
// This statement will be executed
// as if considers one statement by default again below statement is outside of if block
System.out.println("I am Not in if");
}
}Output:
Inside If block
10 is less than 15
I am Not in if
The if statement alone tells us that if a condition is true it will execute a block of statements and if the condition is false it won’t. But what if we want to do something else if the condition is false? Here comes the else statement. We can use the else statement with the if statement to execute a block of code when the condition is false.
if (condition)
{
// Executes this block if
// condition is true
}
else
{
// Executes this block if
// condition is false
}Example:
// Java program to illustrate if-else statement
import java.util.*;
class IfElseDemo {
public static void main(String args[])
{
int i = 10;
if (i < 15)
System.out.println("i is smaller than 15");
else
System.out.println("i is greater than 15");
}
}Output:
i is smaller than 15
A nested if is an if statement that is the target of another if or else. Nested if statements mean an if statement inside an if statement. Yes, java allows us to nest if statements within if statements. i.e, we can place an if statement inside another if statement.
Syntax of the Nested-If statement:
if (condition1)
{
// Executes when condition1 is true
if (condition2)
{
// Executes when condition2 is true
}
}Example:
// Java program to illustrate nested-if statement
import java.util.*;
class NestedIfDemo {
public static void main(String args[])
{
int i = 10;
if (i == 10 || i<15) {
// First if statement
if (i < 15)
System.out.println("i is smaller than 15");
// Nested - if statement
// Will only be executed if statement above
// it is true
if (i < 12)
System.out.println(
"i is smaller than 12 too");
} else{
System.out.println("i is greater than 15");
}
}
}Output:
i is smaller than 15
i is smaller than 12 too
Here, a user can decide among multiple options.The if statements are executed from the top down. As soon as one of the conditions controlling the if is true, the statement associated with that ‘if’ is executed, and the rest of the ladder is bypassed. If none of the conditions is true, then the final else statement will be executed. There can be as many as ‘else if’ blocks associated with one ‘if’ block but only one ‘else’ block is allowed with one ‘if’ block.
Syntax:
if (condition)
statement;
else if (condition)
statement;
.
.
else
statement;Example:
// Java program to illustrate if-else-if ladder
import java.util.*;
class ifelseifDemo {
public static void main(String args[])
{
int i = 20;
if (i == 10)
System.out.println("i is 10");
else if (i == 15)
System.out.println("i is 15");
else if (i == 20)
System.out.println("i is 20");
else
System.out.println("i is not present");
}
}Output:
i is 20
The switch statement is a multiway branch statement. It provides an easy way to dispatch execution to different parts of code based on the value of the expression.
Syntax of Switches:
switch (expression)
{
case value1:
statement1;
break;
case value2:
statement2;
break;
.
.
case valueN:
statementN;
break;
default:
statementDefault;
}Example:
/*package whatever //do not write package name here */
import java.io.*;
class GFG {
public static void main (String[] args) {
int num=20;
switch(num){
case 5 : System.out.println("It is 5");
break;
case 10 : System.out.println("It is 10");
break;
case 15 : System.out.println("It is 15");
break;
case 20 : System.out.println("It is 20");
break;
default: System.out.println("Not present");
}
}
}Output
It is 20
Java supports three jump statements: break, continue and return.
These three statements transfer control to another part of the program.
Terminate a sequence in a switch statement (discussed above).
To exit a loop.
Used as a “civilized” form of goto.
Sometimes it is useful to force an early iteration of a loop. That is, you might want to continue running the loop but stop processing the remainder of the code in its body for this particular iteration. This is, in effect, a goto just past the body of the loop, to the loop’s end. The continue statement performs such an action.
Example:
// Java program to illustrate using
// continue in an if statement
import java.util.*;
class ContinueDemo {
public static void main(String args[])
{
for (int i = 0; i < 10; i++) {
// If the number is even
// skip and continue
if (i % 2 == 0)
continue;
// If number is odd, print it
System.out.print(i + " ");
}
}
}Output
1 3 5 7 9
The return statement is used to explicitly return from a method. That is, it causes program control to transfer back to the caller of the method.
Example
// Java program to illustrate using return
import java.util.*;
public class Return {
public static void main(String args[])
{
boolean t = true;
System.out.println("Before the return.");
if (t)
return;
// Compiler will bypass every statement
// after return
System.out.println("This won't execute.");
}
}Output
Before the return.
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