Java Control Statement

By | October 25th 2019 08:53:41 PM | viewed 99 times

Control Statements

Java If-else Statement

The Java if statement is used to test the condition. It checks boolean condition: true or false. There are various types of if statement in java.

  • if statement
  • if-else statement
  • if-else-if ladder
  • nested if statement

Java if Statement

The Java if statement tests the condition. It executes the if block if condition is true.


if(condition){  
    //code to be executed  
} 
 

Java if-else Statement

The Java if-else statement also tests the condition. It executes the if block if condition is true otherwise else block is executed.

if(condition){  
  //code if condition is true  
}else{  
   //code if condition is false  
}  
 

Using Ternary Operator

We can also use ternary operator (? :) to perform the task of if...else statement. It is a shorthand way to check the condition. If the condition is true, the result of ? is returned. But, if the condition is false, the result of : is returned.

 int number=13;    
    //Using ternary operator  
    String output=(number%2==0)?"even number":"odd number";     
 

Java if-else-if ladder Statement

The if-else-if ladder statement executes one condition from multiple statements.

if(condition1){  
   //code to be executed if condition1 is true  
}else if(condition2){  
  //code to be executed if condition2 is true  
}  
else if(condition3){  
  //code to be executed if condition3 is true  
}  
...  
else{  
//code to be executed if all the conditions are false  
}      
 

Java Nested if statement

The nested if statement represents the if block within another if block. Here, the inner if block condition executes only when outer if block condition is true.

 if(condition){    
        //code to be executed    
    if(condition){  
       //code to be executed    
    }    
}  
 

Java Switch Statement

The Java switch statement executes one statement from multiple conditions. It is like if-else-if ladder statement. The switch statement works with byte, short, int, long, enum types, String and some wrapper types like Byte, Short, Int, and Long. Since Java 7, you can use strings in the switch statement.

In other words, the switch statement tests the equality of a variable against multiple values.

Points to Remember
  • There can be one or N number of case values for a switch expression.
  • The case value must be of switch expression type only. The case value must be literal or constant. It doesn't allow variables.
  • The case values must be unique. In case of duplicate value, it renders compile-time error.
  • The Java switch expression must be of byte, short, int, long (with its Wrapper type), enums and string.
  • Each case statement can have a break statement which is optional. When control reaches to the break statement, it jumps the control after the switch expression. If a break statement is not found, it executes the next case.
  • The case value can have a default label which is optional.
switch(expression){    
case value1:    
  //code to be executed;    
 break;  //optional  
case value2:    
  //code to be executed;    
 break;  //optional  
    ......    
    
default:     
 code to be executed if all cases are not matched;    
}    
 

Java Switch Statement is fall-through

The Java switch statement is fall-through. It means it executes all statements after the first match if a break statement is not present.

 public class SwitchExample2 {  
	public static void main(String[] args) {  
		int number=20;  
		   //switch expression with int value  
		switch(number){  
		   //switch cases without break statements  
		case 10: System.out.println("10");  
		case 20: System.out.println("20");  
		case 30: System.out.println("30");  
		default:System.out.println("Not in 10, 20 or 30");  
		}  
	}  
}  
 
Output:
20
30
Not in 10, 20 or 30

Java Switch Statement with String

Java allows us to use strings in switch expression since Java SE 7. The case statement should be string literal

 public class SwitchStringExample {    
	public static void main(String[] args) {    
		   //Declaring String variable  
		String levelString="Expert";  
		int level=0;  
		   //Using String in Switch expression  
		switch(levelString){    
		   //Using String Literal in Switch case  
		case "Beginner": level=1;  
		break;    
		case "Intermediate": level=2;  
		break;    
		case "Expert": level=3;  
		break;    
		default: level=0;  
		break;  
		}    
		System.out.println("Your Level is: "+level);  
	}    
}   
 

Java Nested Switch Statement

We can use switch statement inside other switch statement in Java. It is known as nested switch statement.

 public class NestedSwitchExample {    
    public static void main(String args[])  
      {  
      //C - CSE, E - ECE, M - Mechanical  
        char branch = 'C';                 
        int collegeYear = 4;  
        switch( collegeYear )  
        {  
            case 1:  
                System.out.println("English, Maths, Science");  
                break;  
            case 2:  
                switch( branch )   
                {  
                    case 'C':  
                        System.out.println("Operating System, Java, Data Structure");  
                        break;  
                    case 'E':  
                        System.out.println("Micro processors, Logic switching theory");  
                        break;  
                    case 'M':  
                        System.out.println("Drawing, Manufacturing Machines");  
                        break;  
                }  
                break;  
            case 3:  
                switch( branch )   
                {  
                    case 'C':  
                        System.out.println("Computer Organization, MultiMedia");  
                        break;  
                    case 'E':  
                        System.out.println("Fundamentals of Logic Design, Microelectronics");  
                        break;  
                    case 'M':  
                        System.out.println("Internal Combustion Engines, Mechanical Vibration");  
                        break;  
                }  
                break;  
            case 4:  
                switch( branch )   
                {  
                    case 'C':  
                        System.out.println("Data Communication and Networks, MultiMedia");  
                        break;  
                    case 'E':  
                        System.out.println("Embedded System, Image Processing");  
                        break;  
                    case 'M':  
                        System.out.println("Production Technology, Thermal Engineering");  
                        break;  
                }  
                break;  
        }  
    }  
}  
 
Output:
Data Communication and Networks, MultiMedia

Java Enum in Switch Statement

Java allows us to use enum in switch statement.

 public class JavaSwitchEnumExample {      
       public enum Day {  Sun, Mon, Tue, Wed, Thu, Fri, Sat  }    
       public static void main(String args[])    
       {    
         Day[] DayNow = Day.values();    
           for (Day Now : DayNow)    
           {    
                switch (Now)    
                {    
                    case Sun:    
                        System.out.println("Sunday");    
                        break;    
                    case Mon:    
                        System.out.println("Monday");    
                        break;    
                    case Tue:    
                        System.out.println("Tuesday");    
                        break;         
                    case Wed:    
                        System.out.println("Wednesday");    
                        break;    
                    case Thu:    
                        System.out.println("Thursday");    
                        break;    
                    case Fri:    
                        System.out.println("Friday");    
                        break;    
                    case Sat:    
                        System.out.println("Saturday");    
                        break;    
                }    
            }    
        }    
}    
 
Output:
Sunday
Monday
Twesday
Wednesday
Thursday
Friday
Saturday

Java Wrapper in Switch Statement

Java allows us to use four wrapper classes: Byte, Short, Integer and Long in switch statement.

public class WrapperInSwitchCaseExample {       
       public static void main(String args[])  
       {         
            Integer age = 18;        
            switch (age)  
            {  
                case (16):            
                    System.out.println("You are under 18.");  
                    break;  
                case (18):                
                    System.out.println("You are eligible for vote.");  
                    break;  
                case (65):                
                    System.out.println("You are senior citizen.");  
                    break;  
                default:  
                    System.out.println("Please give the valid age.");  
                    break;  
            }             
        }  
}  
 
Output:
You are eligible for vote.

Loops in Java

In programming languages, loops are used to execute a set of instructions/functions repeatedly when some conditions become true. There are three types of loops in java.

  • for loop
  • while loop
  • do-while loop

Java For Loop vs While Loop vs Do While Loop

Comparison for loop while loop do while loop
Introduction The Java for loop is a control flow statement that iterates a part of the programs multiple times. The Java while loop is a control flow statement that executes a part of the programs repeatedly on the basis of given boolean condition. The Java do while loop is a control flow statement that executes a part of the programs at least once and the further execution depends upon the given boolean condition.
When to use If the number of iteration is fixed, it is recommended to use for loop. If the number of iteration is not fixed, it is recommended to use while loop. If the number of iteration is not fixed and you must have to execute the loop at least once, it is recommended to use the do-while loop.
Syntax for(init;condition;incr/decr){ // code to be executed } while(condition){ //code to be executed } do{ //code to be executed }while(condition);
Example //for loop for(int i=1;i<=10;i++){ System.out.println(i); } //while loop int i=1; while(i<=10){ System.out.println(i); i++; } //do-while loop int i=1; do{ System.out.println(i); i++; }while(i<=10);
Syntax for infinitive loop for(;;){ //code to be executed } while(true){ //code to be executed } do{ //code to be executed }while(true);
There are three types of for loops in java.
  • Simple For Loop
  • For-each or Enhanced For Loop
  • Labeled For Loop

A simple for loop is the same as C/C++. We can initialize the variable, check condition and increment/decrement value. It consists of four parts:

  1. Initialization: It is the initial condition which is executed once when the loop starts. Here, we can initialize the variable, or we can use an already initialized variable. It is an optional condition.
  2. Condition: It is the second condition which is executed each time to test the condition of the loop. It continues execution until the condition is false. It must return boolean value either true or false. It is an optional condition.
  3. Statement: The statement of the loop is executed each time until the second condition is false.
  4. Increment/Decrement: It increments or decrements the variable value. It is an optional condition.
for(initialization;condition;incr/decr){  
   //statement or code to be executed  
}  

public class ForExample {  
public static void main(String[] args) {  
    //Code of Java for loop  
    for(int i=1;i<=10;i++){  
        System.out.println(i);  
    }  
}  
}  
Java for-each Loop

The for-each loop is used to traverse array or collection in java. It is easier to use than simple for loop because we don't need to increment value and use subscript notation.

It works on elements basis not index. It returns element one by one in the defined variable.

for(Type var:array){  
   //code to be executed  
} 

public class ForEachExample {  
public static void main(String[] args) {  
       //Declaring an array  
    int arr[]={12,23,44,56,78};  
       //Printing array using for-each loop  
    for(int i:arr){  
        System.out.println(i);  
    }  
}  
}    
Java Labeled For Loop

We can have a name of each Java for loop. To do so, we use label before the for loop. It is useful if we have nested for loop so that we can break/continue specific for loop.

Usually, break and continue keywords breaks/continues the innermost for loop only.

for(initialization;condition;incr/decr){  
//code to be executed  
}  

public class LabeledForExample {  
	public static void main(String[] args) {  
		//Using Label for outer and for loop  
		aa:  
			for(int i=1;i<=3;i++){  
				bb:  
					for(int j=1;j<=3;j++){  
						if(i==2&&j==2){  
							break aa;  
						}  
						System.out.println(i+" "+j);  
					}  
			}  
	}  
}      
Output
1 1
1 2
1 3
2 1

Java While Loop

The Java while loop is used to iterate a part of the program several times. If the number of iteration is not fixed, it is recommended to use while loop.

while(condition){  
   //code to be executed  
} 

public class WhileExample {  
public static void main(String[] args) {  
    int i=1;  
    while(i<=10){  
        System.out.println(i);  
    i++;  
    }  
}  
}        
Output
1
2
3
4
5
6
7
8
9
10

Java do-while Loop

The Java do-while loop is used to iterate a part of the program several times. If the number of iteration is not fixed and you must have to execute the loop at least once, it is recommended to use do-while loop.

The Java do-while loop is executed at least once because condition is checked after loop body.


do{  
//code to be executed  
}while(condition); 

public class DoWhileExample {  
public static void main(String[] args) {  
    int i=1;  
    do{  
        System.out.println(i);  
    i++;  
    }while(i<=10);  
}  
}          
Output
1
2
3
4
5
6
7
8
9
10

Java Infinitive do-while Loop

do{  
//code to be executed  
}while(true);

public class DoWhileExample2 {  
public static void main(String[] args) {  
    do{  
        System.out.println("infinitive do while loop");  
    }while(true);  
}  
}              
Output
infinitive do while loop
infinitive do while loop
infinitive do while loop
ctrl+c

Break Statement

When a break statement is encountered inside a loop, the loop is immediately terminated and the program control resumes at the next statement following the loop.

The Java break is used to break loop or switch statement. It breaks the current flow of the program at specified condition. In case of inner loop, it breaks only inner loop.

We can use Java break statement in all types of loops such as for loop, while loop and do-while loop.

Example Java Break Statement with Loop

public class BreakExample {  
public static void main(String[] args) {  
    //using for loop  
    for(int i=1;i<=10;i++){  
        if(i==5){  
            //breaking the loop  
            break;  
        }  
        System.out.println(i);  
    }  
}  
}  


Java Break Statement with Inner Loop
public class BreakExample2 {  
public static void main(String[] args) {  
            //outer loop   
            for(int i=1;i<=3;i++){    
                    //inner loop  
                    for(int j=1;j<=3;j++){    
                        if(i==2&&j==2){    
                            //using break statement inside the inner loop  
                            break;    
                        }    
                        System.out.println(i+" "+j);    
                    }    
            }    
}  
}  

Java Break Statement with Labeled For Loop
public class BreakExample3 {  
public static void main(String[] args) {  
            aa:  
            for(int i=1;i<=3;i++){    
                    bb:  
                    for(int j=1;j<=3;j++){    
                        if(i==2&&j==2){    
                            //using break statement with label  
                            break aa;    
                        }    
                        System.out.println(i+" "+j);    
                    }    
            }    
}  
}  

Java Break Statement in while loop
public class BreakWhileExample {  
public static void main(String[] args) {  
    //while loop  
    int i=1;  
    while(i<=10){  
        if(i==5){  
            //using break statement  
            i++;  
            break;//it will break the loop  
        }  
        System.out.println(i);  
        i++;  
    }  
}  
}  

Java Break Statement in do-while loop
public class BreakDoWhileExample {  
public static void main(String[] args) {  
    //declaring variable  
    int i=1;  
    //do-while loop  
    do{  
        if(i==5){  
           //using break statement  
           i++;  
           break;//it will break the loop  
        }  
        System.out.println(i);  
        i++;  
    }while(i<=10);  
}  
}  

Java Continue Statement

The continue statement is used in loop control structure when you need to jump to the next iteration of the loop immediately. It can be used with for loop or while loop.

The Java continue statement is used to continue the loop. It continues the current flow of the program and skips the remaining code at the specified condition. In case of an inner loop, it continues the inner loop only

We can use Java continue statement in all types of loops such as for loop, while loop and do-while loop.

Example Java Continue Statement Example
public class ContinueExample {  
public static void main(String[] args) {  
    //for loop  
    for(int i=1;i<=10;i++){  
        if(i==5){  
            //using continue statement  
            continue;//it will skip the rest statement  
        }  
        System.out.println(i);  
    }  
}  
}  
Java Continue Statement with Inner Loop
public class ContinueExample2 {  
public static void main(String[] args) {  
            //outer loop  
            for(int i=1;i<=3;i++){    
                    //inner loop  
                    for(int j=1;j<=3;j++){    
                        if(i==2&&j==2){    
                            //using continue statement inside inner loop  
                            continue;    
                        }    
                        System.out.println(i+" "+j);    
                    }    
            }    
}  
}  
Java Continue Statement with Labeled For Loop
public class ContinueExample3 {  
public static void main(String[] args) {  
            aa:  
            for(int i=1;i<=3;i++){    
                    bb:  
                    for(int j=1;j<=3;j++){    
                        if(i==2&&j==2){    
                            //using continue statement with label  
                            continue aa;    
                        }    
                        System.out.println(i+" "+j);    
                    }    
            }    
}  
}  
Output:
1 1
1 2
1 3
2 1
3 1
3 2
3 3
Java Continue Statement in while loop
public class ContinueWhileExample {  
public static void main(String[] args) {  
    //while loop  
    int i=1;  
    while(i<=10){  
        if(i==5){  
            //using continue statement  
            i++;  
            continue;//it will skip the rest statement  
        }  
        System.out.println(i);  
        i++;  
    }  
}  
}  
Java Continue Statement in do-while loop
public class ContinueDoWhileExample {  
public static void main(String[] args) {  
    //declaring variable  
    int i=1;  
    //do-while loop  
    do{  
        if(i==5){  
                //using continue statement  
                 i++;  
            continue;//it will skip the rest statement  
        }  
        System.out.println(i);  
        i++;  
    }while(i<=10);  
}  
}  
Output:

2
3
4
6
7
8
9
10

Java Comment

Java Single Line Comment
     //This is single line comment  
 
Java Multi Line Comment
    /* 
    This  
    is  
    multi line  
    comment 
    */  
 
Java Documentation Comment
    /** 
    This  
    is  
    documentation  
    comment 
    */   
 
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