Control flow

Agenda:

• Selection statements
• Iterative statements
• Transfer statements

Selection statements:

• if-else
• switch

if-else:
Syntax:

1.  if(b){// here b is boolean type
2. // action if b is true.
3. }else{
4. action if b is false.
5. }

• The argument of the if statement must be boolean type otherwise you will get a compiler error.
• {} curly braces are optional if you take only one statement under if, but it should not be a declarative statement.
• e.g if(10>5)
• int x=10;// Compiler error because it is a declarative statement.
• if(true); is valid syntax but not useful.

switch:
If many options are available then it is not recommended to use if-else, you should go for the switch statement.
Syntax:

1. switch(x){
2. case 1: action1
3. case 2: action2
4. case 3: action3
5. .
6. .
7. .
8. default: default action
9. }

• {} curly braces are mandatory.
• case and default are optional
• Every statement inside the switch must be under some case or default. Independent statements are not allowed.
• e.g switch(){
• System.out.println("Hello");// It is an independent statement so, compiler error.
• }

byte,short,int,char,Byte,Short,Integer,Character,enum,String are allowed argument for switch.
Every case label should be compile-time constant otherwise you will get a compiler error.
e.g int x=10;
switch(x){
case x: System.out.println("Hello");//compiler error because x is not compile time constant. to make it compile time constant use  final keyword.
}
final int x =10;//compile time constant
switch(x){
case x: System.out.println("Hello");
}
Switch argument and case label can be expression, but case must be constant expression.
Every case label should be within the range of switch argument types.
byte b=10;
switch(b){
case 10:System.out.println("anu");
case 100: System.out.println("ambe");
case 1000: System.out.println("amit");//compiler error, byte range is -128 to 127  but case label 1000 which is out of range
}
Duplicate case label is not allowed.

Fall through inside the switch:

• Within the switch statement if any case is matched from that case onwards all statements will be executed until the end of the switch or break.
• Within the switch, you can take the default anywhere.

Iterative statements:
while loop:

• If you don't know the number of iterations in advance then you should go for a while loop.
• The argument of the while loop must be boolean type, otherwise compiler error.
• {} curly braces are optional and without curly braces, you can take only one statement which should not be a declarative statement(int a =10; or int a)

do-while loop:

• If you want to execute while loop at least one then you should go for a do-while loop.
• {} curly braces are optional and without curly braces, you can take only one statement between do and while which should not be a declarative statement(int a =10; or int a).

Syntax:
do{}while(b);// semicolon is mandatory.
Note: do while(b);//compiler error

For loop:
If you know the number of iteration in advance then you can use this.
syntax:

{} curly braces are optional and without curly braces, you can take only one statement which should not be a declarative statement(int a =10; or int a)
1.Initialization section

• This section will be executed only once.
• Here you can declare loop variable and you will perform initialization.
• You can declare multiple variables but should be of the same type.
• You can't declare the different types of variables.
• In the initialization section, you can take any valid statement including System.out.println().

2. condition check

• You can take any java expression but should be of the type boolean.
• The condition expression is optional if you are not taking any expression compiler will place true.

3.Increment and decrement section:
Here you can take any java statement including System.out.println().

Enhance for loop:

• It was introduced in java 1.5v.
• Best suitable to retrieve the elements of arrays and collection.
• Example:
• int a[] ={10,20,30,40,50};
• for(int val:a){
• System.out.println(val);
• }

Transfer statements
Break statement:

• You can use break statement in the following cases.
• Inside switch to stop fall-through.
• Inside loops to break the loop based on some condition.
• Inside label, blocks to break block execution based on some condition.
• If you are using anywhere else you will get a compiler error.

Continue statement:

• You can use continue statement to skip current iteration and continue for the next iteration.
• You can use continue statement only inside loops otherwise you will get a compiler error.

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