The document discusses various flow control statements in Java including if-else statements, while loops, do-while loops, for loops, break and continue statements, return statements, and switch statements. It provides examples of how to use each statement and explains their functionality such as only executing the contents of an if block if the condition is true or always executing the do block once in a do-while loop.

1. Basic Java Programming
Sasidhara Marrapu

2. Execution Flow Control
 Control Flow  Lab Problem
 Home Work

3. Execution Control
To do or not to do
that is the question.

4. If
if( ) { } else { }

5. if( ) { } else { }
// Do this stuff
if (a <= b && x != 4) {
// Do this if true
}
else {
// Do this if false
}
// Do this stuff
Any expression with
a boolean result.

6. if( ) { } else { }
Example
// Do this stuff
if (a <= b && x != 4) {
x = x * a;
z = b * 2;
}
else {
b = z / 2;
a = 3;
}
// Do this stuff

7. if( ) { } else { }
Brackets not always Required
// Do this stuff
if (a <= b && x != 4) {
// Do this if true
}
else {
// Do this if false
}
// Do this stuff
{ } not needed if there
is only a single statement.

8. if( ) { } else { }
Example
// Do this stuff
if (a <= b && x != 4)
x = x * a;
else
b = z / 2;
// Do this stuff

9. if() {} else {}
Optional else
// Do this stuff
if (a <= b && x != 4) {
// Do this if true
}
else {
// Do this if false
}
// Do this stuff The else clause
is optional.

10. if( ) { } else { }
Example
// Do this stuff
if (a <= b && x != 4) {
x = x * a;
z = b * 2;
}
// Do this stuff

11. if( ) { } else { }
Example with Single Statement
// Do this stuff
If (a <= b && x != 4)
x = x * a;
// Do this stuff
// Do this stuff
if (a <= b && x != 4) x = x * a;
// Do this stuff

12. if( ) { } else { }
A string of ifs
// Do this stuff
if (a <= b) {
// Do this if a <= b
}
else if ( r > 5 ) {
// Do this if !(a <= b) && r > 5
}
else {
// Do this if !(a <= b) && !(r > 5)
}
// Do this stuff

13. if( ) { } else { }
Nesting ifs
// Do this stuff
if (a <= b) {
// Do this if a <= b
if ( r > 5 ) {
// Do this if a <= b && r > 5
} else {
// Do this if !(a <= b) && !(r >
5)
}
}
// Do this stuff

14. The Looping Statements
while ( ) { }
do { } while ( )
for ( ; ; ) { }

15. while ( ) { }
// Do this stuff
while (a <= b) {
// Do this while a <= b
}
// Do this stuff
Any expression with a boolean
result. The contents of the loop
are only executed while true.

16. while ( ) { }

17. while ( ) { }
Example
// Do this stuff
i = 1;
while (i <= 5) {
System.out.println("i = " + i);
i++;
}
// Do this stuff i = 1
i = 2
i = 3
i = 4
i = 5
>

18. while ( ) { }
Example
// Do this stuff
i = 1;
while (i <= 5) {
System.out.println("i = " + i);
i++;
}
// Do this stuff
// Do this stuff
i = 1;
while (i <= 5) {
System.out.println("i = " + i++);
}
// Do this stuff
// Do this stuff
i = 1;
while (i <= 5) System.out.println("i = " + i++);
// Do this stuff
i = 1
i = 2
i = 3
i = 4
i = 5
>

19. do { } while ( )

20. do { } while ( )
// Do this stuff
do {
// Do this while a <= b
} while (a <= b)
// Do this stuff
Any expression with a boolean
result. The contents of the loop
are always executed once and
then only executed if true.

21. do { } while ( )
Example
// Do this stuff
i = 6;
do {
System.out.println("i = " + i);
i--;
} while (i <= 5 && i > 0)
// Do this stuff
i = 6
i = 5
i = 4
i = 3
i = 2
i = 1
>

22. for loop

23. for ( ; ; ) { }
// . . .
for (i = 1; i < 5; i++) {
System.out.println("i = " + i);
}
// . . .
Initialization(s) executed once
before the for loop is entered.
Any expression with a boolean
result. The contents of the loop
are only executed if true.
Statement(s) that
increment variables
used in the for loop.

24. for ( ; ; ) { }
// . . .
for (i = 1; i < 5; i++) {
System.out.println("i = " + i);
}
// . . .
i = 1
i = 2
i = 3
i = 4
>

25. for ( ; ; ) { }
// . . .
for (i = 1, j = 4; i < 5; i++, j--) {
System.out.println("i, j = " + i + ", "
+ j);
}
// . . .
i, j = 1, 4
i, j = 2, 3
i, j = 3, 2
i, j = 4, 1
>
Initializations separated by a comma.
Statements separated by a commas.

26. for each { }
// . . .
for(data_type item : collection) {
...
}
Data type of Item in the collection
Collection of Items.

27. break and continue
// . . .
int i = 0;
while (true) {
i++;
System.out.println("i = " + i);
if (i == 2) continue;
System.out.println("No continue " +
i);
if (i >= 4) break;
System.out.println("No break " + i);
}
// . . .

28. break and continue Example
// . . .
int i = 0;
while (true) {
i++;
System.out.println("i = " + i);
if (i == 2) continue;
System.out.println("No continue " +
i);
if (i >= 3) break;
System.out.println("No break " + i);
}
// . . .
i = 1
No continue 1
No break 1
i = 2
i = 3
No continue 3
>

29. Labeled break and continue
// . . .
int i = 0;
outer:for (int k = 10; k < 99; k++) {
while (true) {
i++;
System.out.println("i, k = " + i", " + k);
if (i == 2) continue outer;
System.out.println("No continue " + i);
if (i >= 3) break outer;
System.out.println("No break " + i);
}
}
// . . .
The label must immediately precede the loop.

30. i, k = 1, 10
No continue 1
No break 1
i, k = 1, 10
No continue 1
No break 1
i, k = 2, 10
i, k = 1, 10
No continue 1
No break 1
i, k = 2, 10
i, k = 3, 11
No continue 3
>
Labeled break and continue
Example
// . . .
int i = 0;
outer:for (int k = 10; k < 20; k++) {
while (true) {
i++;
System.out.println("i, k = " + i", " + k);
if (i == 2) continue outer;
System.out.println("No continue " + i);
if (i >= 3) break outer;
System.out.println("No break " + i);
}
}
// . . .

31. return
• In a method the return statement "breaks" out of the method.
• It can be used to break out of a loop and the method.

32. The switch Statement
switch ( ) { }

33. Must be an expression that evaluates
to an int, byte, short or char.
Must be an constant expression that evaluates
at compile time. No variables allowed.
default is a keyword.
switch is a keyword.
case is a keyword.
switch ( ) { }
// . . .
switch ( i ){
case 1 : System.out.println("one"); break;
case 2 : System.out.println("two"); break;
case 4 : System.out.println("four"); break;
default: System.out.println("default");
}
// . . .

34. default
default
one
default
one
two
default
one
two
default
switch ( ) { }
Execution Flow
// . . .
for (int i = 0, i < 5, i++) {
switch ( i ){
case 1 : System.out.println("one"); break;
case 2 : System.out.println("two"); break;
case 4 : System.out.println("four"); break;
default: System.out.println("default");
}
}
// . . .
default
one
two
default
four
>

35. switch ( ) { }
The default case is optional
// . . .
for (int i = 0, i < 5, i++) {
switch ( i ){
case 1 : System.out.println("one"); break;
case 2 : System.out.println("two"); break;
case 4 : System.out.println("four"); break;
}
}
// . . .
one
two
four
>

36. switch ( ) { }
With some missing breaks
// . . .
for (int i = 0, i < 5, i++) {
switch ( i ){
case 1 : System.out.println("one"); break;
case 2 : System.out.println("two"); break;
case 4 : System.out.println("four"); break;
default: System.out.println("default");
}
}
// . . .
// . . .
for (int i = 0, i < 5, i++) {
switch ( i ){
case 1 : System.out.println("one");
case 2 : System.out.println("two");
case 4 : System.out.println("four"); break;
default: System.out.println("default");
}
}
// . . .
default
default
one
two
four
default
one
two
four
two
four
default
one
two
four
two
four
default
default
one
two
four
two
four
default
four
default
one
two
four
two
four
default
four
>

37. switch ( ) { }
Using missing breaks
char c;
// . . .
switch ( c ){
case 'a':
case 'e':
case 'i':
case 'o':
case 'u': System.out.println("vowel"); break;
default: System.out.println("consonant");
}
// . . .

38. switch ( ) { }
Format Alternatives
// . . .
for (int i = 0, i < 5, i++) {
switch ( i ){
case 1 : System.out.println("one"); break;
case 2 : System.out.println("two"); break;
case 4 : System.out.println("four"); break;
default: System.out.println("default");
}
}
// . . .
// . . .
for (int i = 0, i < 5, i++) {
switch ( i ){
case 1 : System.out.println("one");
break;
case 2 : System.out.println("two");
break;
case 4 : System.out.println("four");
break;
default: System.out.println("default");
}
}
// . . .
// . . .
for (int i = 0, i < 5, i++) {
switch ( i ){
case 1 : System.out.println("one"); break;
case 2 : {
System.out.print("t");
System.out.print("w");
System.out.println("o");
} break;
case 4 : System.out.println("four"); break;
default: System.out.println("default");
}
}
// . . .

39. Summary
•if ( ) { } else { }
•while ( ) { }
•do { } while ( )
•for ( ; ; ) { }
•break and continue
•return
•switch ( ) { }

40. Home Work