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Merge pull request #54 from ananya0504/io-conditionals-switch-stmt
Fixed issue: io-conditionals.md (Improved switch statement)
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‎lessons/images/java-switch-statement.png

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‎lessons/io-conditionals.md

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@@ -109,7 +109,7 @@ Let's go through the code line by line.
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Switch statements are used to execute different code depending on the value of a variable. We use Switch statements for the condition based problem solving. Switch statements are used when we have multiple conditions in a single if statement. It is just a substitute for multiple if-else statements. In this a variable is compared to multiple cases one by one and when the case is matched then the code block under that case will be executed.
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#### Semantics
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#### Syntax
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```java
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// syntax
@@ -126,29 +126,173 @@ Switch statements are used to execute different code depending on the value of a
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break;
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}
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```
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Above is the basic syntax of switch statements. This is how it works:
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- The switch expression is only evaluated `once`.
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- The value of the expression is `compared` with the values of each case value.
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- If there is a `match`, ie. the case value and the switch expression are same, the associated block of code with the case value is executed.
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- The `break` and `default` keywords are optional and will be explained ahead.
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Now, let us see a diagramtic workflow of the Java Switch statement for a better understanding.
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Above is the basic syntax of switch statements. Let's see some examples to understand it better.
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![java-switch-statement](./images/java-switch-statement.png)
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Let us see an example to understand it better.
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```java
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// print hello world in different languages using switch statement
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// Program to check Vowel or Consonant:
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// It is not case-sensitive.
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public class <ClassName> {
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public static void main(String[] args){
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int a = 10;
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switch(a){
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case 1:
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System.out.println("Hello");
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break;
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case 2:
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System.out.println("Namastey");
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break;
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case 3:
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System.out.println("Hola");
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break;
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default:
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System.out.println("learning more");
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char ch='O';
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switch(ch)
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{
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case 'a':
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System.out.println("Vowel");
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break;
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case 'e':
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System.out.println("Vowel");
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break;
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case 'i':
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System.out.println("Vowel");
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break;
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case 'o':
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System.out.println("Vowel");
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break;
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case 'u':
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System.out.println("Vowel");
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break;
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case 'A':
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System.out.println("Vowel");
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break;
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case 'E':
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System.out.println("Vowel");
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break;
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case 'I':
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System.out.println("Vowel");
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break;
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case 'O':
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System.out.println("Vowel");
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break;
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case 'U':
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System.out.println("Vowel");
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break;
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default:
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System.out.println("Consonant");
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break;
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}
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}
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}
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Output : Vowel
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```
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#### The 'break' Keyword
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- When the Java compiler reaches a `break` keyword, it breaks out of the switch block.
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- This will stop the execution of more code and case testing inside the block.
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- Basically it means that When a match is found, and the job is done, there is no need for more testing. Hence we break out of the switch statement.
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#### The 'default' Keyword
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- The `default` keyword specifies some code to run if there is no case match:
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Now let us see another example where there are no break statements present:
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```java
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//switch cases without break statements
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public class SwitchExample2 {
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public static void main(String[] args) {
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int num = 20;
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switch(num){
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case 10:
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System.out.println("10");
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case 20:
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System.out.println("20");
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case 30:
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System.out.println("30");
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default:
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System.out.println("The number is not 10, 20 or 30");
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}
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}
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}
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Output : 20
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30
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The number is not 10, 20 or 30
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```
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Remember that the switch statement is `fall-through`. That's why all the statements got executed after the first match because the break statement is NOT present.
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#### Points to Remember
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- There can be 1 or N number of `case values` for a switch expression.
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- The `case values` must be `literal` or `constant`. It doesn't allow variables.
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- The `case values` must be `unique`. In case of duplicate value, it renders compile-time error.
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- The Java `switch expression` must be of `byte, short, int, long` (with its Wrapper type), `enums and string`.
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- 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.
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- The case value can have a `default` label which is `optional`.
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- The Java switch statement is `fall-through`. It means it executes all statements after the first match if a break statement is NOT present.
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#### Java Nested Switch Statements
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We can use switch statement inside other switch statement in Java. It is known as nested switch statement.
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```java
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//Java Program to demonstrate the use of Java Nested Switch
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public class NestedSwitchExample {
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public static void main(String args[])
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{
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//C - CSE, E - ECE, M - Mechanical
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char branch = 'C';
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int collegeYear = 4;
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switch(collegeYear)
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{
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case 1:
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System.out.println("English, Maths, Science");
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break;
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case 2:
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switch( branch )
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{
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case 'C':
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System.out.println("Operating System, Java, Data Structure");
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break;
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case 'E':
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System.out.println("Micro processors, Logic switching theory");
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break;
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case 'M':
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System.out.println("Drawing, Manufacturing Machines");
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break;
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}
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break;
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case 3:
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switch(branch)
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{
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case 'C':
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System.out.println("Computer Organization, MultiMedia");
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break;
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case 'E':
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System.out.println("Fundamentals of Logic Design, Microelectronics");
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break;
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case 'M':
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System.out.println("Internal Combustion Engines, Mechanical Vibration");
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break;
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}
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break;
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case 4:
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switch(branch)
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{
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case 'C':
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System.out.println("Data Communication and Networks, MultiMedia");
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break;
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case 'E':
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System.out.println("Embedded System, Image Processing");
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break;
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case 'M':
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System.out.println("Production Technology, Thermal Engineering");
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break;
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}
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break;
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}
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}
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}
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Output : Data Communication and Networks, MultiMedia
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```
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