Flow control describes the order in which all the statements
will execute at run time
Selection Statements
1.if-else :
- The argument in the if statement Should be ‘boolean’. If we provide other datatype, it will generate Compile time Error
int
x=0;
if
(x) {
System.out.println("Hello");
} else
{
System.out.println("Hi");
}
incompatible types: int cannot be
converted to boolean
|
boolean b=false;
if (b=true) {
System.out.println("Hello");
} else {
System.out.println("Hi");
}
//o/p Hello
|
- In the case of if-else statements else part & curly braces are optional.Without curly braces we are allowed to take 1 statement under ‘if’, that statement never be declarative statement other wise compile time error.
Syntax:
int i = 0;
switch (i) {
case 1:
ACTION
1;
case 2:
ACTION
2;
case n:
ACTION
N;
default:
Def.
Action
}
- Curly bases are mandatory.
- Inside a Switch both case and default are optional
int
i = 10;
switch
(i)
{
// CORRECT
}
int
i = 10;
switch(i)
{
System.out.println("Hello");
}
//CE : error: case, default, or '}'
expected
- All Integer Datatypes(int, short except floating point datatypes), Wrapper Classes, enums (1.5v ), Strings(1.7v) are allowed in switch statements.
- Case labels must be compiled time constants(final variables), variables are not allowed.
int i = 10; //final int i=10 - No Error
switch (i) {
case i:
System.out.println("Hello");
break;
}
error: constant expression required : case
i:
^
- The ‘case’ labels must be in the range supported by switch argument.
byte b = 100;
switch (b)
{
case 10 :System.out.println("10");
break;
case 100 :System.out.println("100");
break;
case 1000
:System.out.println("1000");
break;
}
error: incompatible types: possible
lossy conversion from int to byte
- The case labels and the switch arguments can be expressions also but case label must be constant expression
int
x=10, y=10;
byte
b = 100;
switch
(b + 1) {
case
10:
System.out.println("10");
case
20:
System.out.println("20");
case
30 + 40:
System.out.println("30+40 = 70");
case x + y:
System.out.println("30+40 =
70"); //ERROR
}
Test.java:16: error: constant
expression required
case x + y:
^
- Duplicate case labels are not allowed.
- default Case: In the switch statement we can place default case any where but it is convention to take default case always at least.
- In side switch once we got matched case from that statement on words all the statements will execute from top to bottom until break or end of switch
switch (x)
{
default:
System.out.println("default");
case 0:
System.out.println("0");
break;
case 1:
System.out.println("1");
case 2:
System.out.println("2");
}
Here if ‘x’ is 0 then output is 0.
if ‘x’ is 1 then output is 1,2.
if ‘x’ is 2 then output is 2.
if ‘x’ is 3 then output is default.
Iterative Statements
1.While:
Syntax:
while(boolean){
//statements…
}
- The argument in the while Statement Should be Boolean, otherwise we will get C.E
- curly braces are optional.Without curly braces we are allowed to take 1 statement under ‘while’, that statement never be declarative statement other wise compile time error.
- If we wrote boolean argument as Constant value, it leads to “UnReachable Statement”
while (true) {
System.out.println("hi");
}
System.out.println("Hello");
Test.java:12: error: unreachable statement
System.out.println("Hello");
^
|
while (false) {
System.out.println("hi");
}
System.out.println("Hello");
Test.java:4: error: unreachable tatement System.out.println("hi");
^
|
- If we wrote any final Constant expression, it leades to infinite loop & the next statement after while will be “UnReachable Statement”
int a = 10;
int b = 20;
while(a<b)
{
System.out.println("Hi");
}
System.out.println("Hello");
Output
: Hi Hi Hi …. Infinite loop, no error
|
final int a = 10;
final int b = 20;
while(a<b)
{
System.out.println("Hi");
}
System.out.println("Hello");
Test.java:4: error: unreachable tatement System.out.println("Hello");
^
|
2.do-while:
In the loop body has to execute at least once then we should
go for do-while loop.
Syntax: Here ‘;’ is
mandatory.
do
{
}while (boolean);
- Curly braces are optional, with out curly braces we should take only 1 statement b/w do-while, that statement never be declarative statement
do
System.out.println("hi");
while (a>b);
|
do
while(a>b);
//Error: atleaset
one statement required
|
do;
while(a>b);
//; is valid statement
|
- Like while, we will get Unreachable statement error, in following case
final int a = 10;
final int b = 20;
do
{
System.out.println("Hi");
}
while (a<b);
System.out.println("Hello");
3.for :
- The most commonly used loop
- All the 3 parts of for loop are independent of each other & optional.
for( ; ;); //valid
- Curly braces are optional, with out curly braces we should take only 1 statement, that statement never be declarative statement.
a. Initialization Section
- This will be executed only once
- Here we can declare multiple variables of same type, but multiple variables of different types are not allowed. Because break between the variables leads to C.E
for
( int x=10, y=20
; ; ) // No Error
for
( int x=10, byte y=20 ; ; ) // ERROR :
error: <identifier> expected
- In the initialization section we can take any valid java statement, including s.o.p also.
int i = 0;
for(System.out.println("Hi");
i<5; i++)
{
System.out.print("Hello");
}
//O/p : Hi, Hello …(5 times)
b. Conditional Expression
- Here We can take any valid Conditional expression, but result should be boolean type.
- Conditional statement is Optional; if wont specify any thing, default should be ‘TRUE’
c. Increment/Decrement
- This statement also Optional.
- In this section we can take any valid java statement, including s.o.p also.
- Unreachable Statement
for(int i = 0; ; i++)
{
System.out.println("Hello");
}
System.out.println("Hi");
// unreachable statement
System.out.println("Hi");
|
for(int i = 0;false;i++)
{
System.out.println("Hello");
}
System.out.println("Hi");
// unreachable statement System.out.println("Hello");
|
final int a = 10,b = 20;
for(int i = 0;a<b; i++)
{
System.out.println("Hello");
}
System.out.println("Hi");
// unreachable statement System.out.println("hi");
|
Transfer Statements
1.break :
It can be
used in the following places.
·
with in
the loops to come out of the loop.
·
inside
switch statement to come out of the switch .
·
If we are using break any where else we will get a compile
time error.
int x = 0;
if(x!=5)
break;
System.out.println("if");
C.E: error:
break should not outside switch or loop
2.continue:
- we should use ‘continue’ only in the loops to skip current iteration & continue for the next iteration.
- If we are using ‘continue’ any where except loops we will get compile time error saying, “continue out side of loop”.
for(int i=0;i<10;i++)
{
if((i%2) == 0)
continue;
System.out.print(i);
}
O/P:- 13579
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