Transcript Class Exercise - Gadjah Mada University

Control Statement
Pemrograman Dasar
Smt I 2004/2005
Statement (review)
The statement is the main building block
from which code sequences are
constructed.
 Statements are executed in the order
listed and are always terminated by a
semicolon.

expr;
or
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{ expr1; Control
expr2;
Statements … exprn; }
2
Control Flow Statement


We use control flow statement to conditionally execute
statements, to repeatedly execute a block of statements,
and to otherwise change the normal, sequential flow of
control.
For example, in the following code snippet, the if statement
conditionally executes the System.out.println statement
within the braces, based on the return value of
Character.isUpperCase(aChar):
char c;
... if (Character.isUpperCase(aChar))
{ System.out.println("The character " + aChar + " is upper case."); }
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Control Flow Statement in Java
Statement Type
Keyword
Looping
while, do-while , for
Decision making
if-else, switch-case
Exception handling
try-catch-finally, throw
branching
break, continue, label:,
return
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The if Statement


used to conduct a conditional test and execute a
block of statements if the test evaluates to true.
Syntax:
if ( booleanExpression ) {statement}
if ( booleanExpression )
{ statement }
else
{ statement }

Note you can layout code in any way you want.
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Example If Else
public class IfElseDemo {
public static void main(String[] args) {
int testscore = 76;
char grade;
if (testscore >= 90) {
grade = 'A';
} else if (testscore >= 80)
grade = 'B';
} else if (testscore >= 70)
grade = 'C';
} else if (testscore >= 60)
grade = 'D';
} else {
grade = 'F';
}
System.out.println("Grade =
{
{
{
" + grade);
}
}
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


The output from this program is: Grade = C
You may have noticed that the value of testscore
can satisfy more than one of the expressions in
the compound if statement: 76 >= 70 and 76 >=
60.
However, as the runtime system processes a
compound if statement such as this one, once a
condition is satisfied, the appropriate statements
are executed (grade = 'C';), and control passes
out of the if statement without evaluating the
remaining conditions.
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Example If Else 2
import java.util.*;
public class Morning {
public static void main( String args[] ) {
Calendar rightNow = Calendar.getInstance();
if ( rightNow.get( Calendar.AM_PM ) == Calendar.AM )
System.out.println( "Good morning..." );
else
System.out.println( "Good afternoon..." );
}
}
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Dangling Else
if ( booleanExpression )
if ( booleanExpression )
statement
else
statement

The else clause is always associated with
the nearest if

Use { … } to change the association
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The switch statement



used to evaluate a variable that can later be
matched with a value specified by the "case"
keyword in order to execute a group of
statements.
The default case is optional.
Syntax:
switch ( expression ) {
case char/byte/short/int constant : statementSequence
…
default: statementSequence
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Example
public class SwitchDemo {
public static void main(String[] args) {
int month = 8;
switch (month) {
case 1: System.out.println("January"); break;
case 2: System.out.println("February"); break;
case 3: System.out.println("March"); break;
case 4: System.out.println("April"); break;
case 5: System.out.println("May"); break;
case 6: System.out.println("June"); break;
case 7: System.out.println("July"); break;
case 8: System.out.println("August"); break;
case 9: System.out.println("September"); break;
case 10: System.out.println("October"); break;
case 11: System.out.println("November"); break;
case 12: System.out.println("December"); break;
}
}
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}
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public class SwitchDemo2 {
public static void main(String[] args) {
int month = 2; int year = 2000; int numDays = 0;
switch (month) {
case 1:
case 3:
case 5:
case 7:
case 8:
case 10:
case 12:
numDays = 31;
break;
case 4:
case 6:
case 9:
case 11:
numDays = 30;
break;
case 2:
if ( ((year % 4 == 0) && !(year % 100 == 0))
|| (year % 400 == 0) )
numDays = 29;
else
numDays = 28;
break; }
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System.out.println("Number
of Days = " + numDays); }
}
Example
12
Switch-Example 3
We use the default statement at the end of the switch to handle all
values that aren't explicitly handled by one of the case statements.
int month = 8;
. . .
switch (month) {
case 1: System.out.println("January"); break;
case 2: System.out.println("February"); break;
case 3: System.out.println("March"); break;
case 4: System.out.println("April"); break;
case 5: System.out.println("May"); break;
case 6: System.out.println("June"); break;
case 7: System.out.println("July"); break;
case 8: System.out.println("August"); break;
case 9: System.out.println("September"); break;
case 10: System.out.println("October"); break;
case 11: System.out.println("November"); break;
case 12: System.out.println("December"); break;
default: System.out.println("Hey, that's not a valid month!");
break;
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}
The while Loop


While : “used to declare a loop that iterates a
block of statements. The loop`s exit condition is
specified as part of the while statement.”
Syntax:
while ( booleanExpression ){
statement
}
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Divide
public class Divide {
public static void main( String args[] ) {
int dividend = 35;
int divisor = 5;
int remainder = dividend;
int quotient = 0;
while ( remainder >= divisor ) {
remainder = remainder - divisor;
quotient = quotient + 1;
}
System.out.println(
dividend + " / " + divisor + " = " + quotient);
System.out.println(
dividend + " % " + divisor + " = " + remainder );
}
} // Divide
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Square Root
public class SquareRoot {
public static void main( String args[] ) {
double epsilon = 1.0e-9;
double number = 2.0;
double oldGuess = 0;
double newGuess = number;
while ( Math.abs( newGuess - oldGuess ) > epsilon ) {
oldGuess = newGuess;
newGuess = ( ( number / oldGuess ) + oldGuess ) / 2.0;
}
System.out.println(
“The square root of “ + number + “ is “ +newGuess );
}
} // SquareRoot
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The do-while Loop
do-while evaluates the expression at the
bottom. Thus the statements associated
with a do-while are executed at least
once.
 Syntax:

do {
statement(s)
}
while ( booleanExpression );
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The for Loop

Syntax:
for (initialization; termination; increment) {
statement
}




The initialization is an expression that initializes
the loop-it's executed once at the beginning of
the loop.
The termination expression determines when to
terminate the loop. This expression is evaluated
at the top of each iteration of the loop. When the
expression evaluates to false, the loop
terminates.
Finally, increment is an expression that gets
invoked after each iteration through the loop.
Each of the expressions is optional, the
semicolons are not.
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

Often for loops are used to iterate over the elements in an
array, or the characters in a string.
The following sample, ForDemo, uses a for statement to
iterate over the elements of an array and print them:
public class ForDemo { public static void main(String[] args){
int[] arrayOfInts = {32, 87, 3, 589, 12, 1076, 2000, 8, 622, 127 };
for (int i = 0; i < arrayOfInts.length; i++) {
System.out.print(arrayOfInts[i] + " ");
}
System.out.println();
}
} 7/21/2015 2:22 AM
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Factorial
public class Factorial {
public static void main( String args[] ) {
int num = 5;
int fact = 1;
for ( int i = 1; i <= num; i++ )
fact = fact * i;
System.out.println( fact );
}
} // Factorial
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CharCount
public class CharCount {
public static void main( String args[] ) {
String theString = "Now is the time for all good people ... ";
char target = 't';
int count = 0;
for ( int i = 0; i < theString.length(); i++ )
if ( theString.charAt( i ) == target ) count++;
System.out.println( target + " appears " + count + " times" );
}
} // CharCount
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Reverse
// This program reverses a given string
public class Reverse {
public static void main( String args[] ) {
String orig = "Hello World";
String reverse = "";
for (int i = 0; I < orig.length(); i++)
reverse = orig.charAt( i ) + reverse;
System.out.println( reverse );
}
} // Reverse
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Mult
public class Mult {
public static void main( String args[] ) {
for ( int i = 0; i < 10; i++ ) {
for ( int j = 0; j < 10; j++ ) {
if ( i * j < 10 ) System.out.print( " " );
System.out.print( ( i * j ) + " " );
}
System.out.println();
}
}
} // Mult
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Transfer Statements
The break statement can occur anywhere
within a switch, for, while or do
statement and causes execution to jump
to the next statement.
 The continue statement can occur
anywhere within a for, while or do
statement and causes execution to jump
to the end of the loop body.

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Exception Handling Statements



Exception is an event during program execution
that prevents the program from continuing
normally; generally, an error.
It means that the normal flow of the program is
interrupted and that the runtime environment
attempts to find an exception handler--a block of
code that can handle a particular type of error.
The exception handler can attempt to recover
from the error or, if it determines that the error is
unrecoverable, provide a gentle exit from the
program.
The Java supports exceptions with the try, catch,
and throw keywords.
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Try-Catch-finally




Three statements play a part in handling
exceptions:
The try statement identifies a block of
statements within which an exception might be
thrown.
The catch statement must be associated with a
try statement and identifies a block of statements
that can handle a particular type of exception.
The statements are executed if an exception of a
particular type occurs within the try block.
The finally statement must be associated with a
try statement and identifies a block of statements
that are executed regardless of whether or not an
error occurs within the try block.
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Exception Handling

Syntax
try {
statement(s)
} catch (exceptiontype name) {
statement(s)
} finally {
statement(s)
}
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Branching Statement

Java support 3 branching statement:



The break statement
The continue statement
The return statement
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Branching #1 : Break




The break statement has two forms: unlabeled
and labeled.
The unlabeled form of the break statement used
with switch earlier. Unlabeled break terminates
the enclosing switch statement, and flow of
control transfers to the statement immediately
following the switch.
We can also use the unlabeled form of the break
statement to terminate a for, while, or do-while
loop.
The following sample program, BreakDemo ,
contains a for loop that searches for a particular
value within an array:
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Unlabeled-Break Example
public class BreakDemo {
public static void main(String[] args) {
int[] arrayOfInts = { 32, 87, 3, 589, 12, 1076,
2000, 8, 622, 127 };
int searchfor = 12;
int i = 0;
boolean foundIt = false;
for ( ; i < arrayOfInts.length; i++) {
if (arrayOfInts[i] == searchfor) {
foundIt = true;
break;
}
}
if (foundIt) {
System.out.println("Found " + searchfor + " at index " + i);
} else {
System.out.println(searchfor + "not in the array");
}
}
}
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Branching: Labeled-Break
The labeled form terminates an outer
statement, which is identified by the label
specified in the break statement.
 The following program,
BreakWithLabelDemo, is similar to the
previous one, but it searches for a value in
a two-dimensional array. Two nested for
loops traverse the array. When the value
is found, a labeled break terminates the
statement labeled search, which is the
outer for loop:

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public class BreakWithLabelDemo {
public static void main(String[] args) {
int[][] arrayOfInts = { { 32, 87, 3, 589 },
{ 12, 1076, 2000, 8 },
{ 622, 127, 77, 955 }
};
int searchfor = 12;
int i = 0;
int j = 0;
boolean foundIt = false;
search:
for ( ; i < arrayOfInts.length; i++) {
for (j = 0; j < arrayOfInts[i].length; j++) {
if (arrayOfInts[i][j] == searchfor) {
foundIt = true;
break search;
}
}
}
if (foundIt) {
System.out.println("Found " + searchfor + " at " + i + ", " + j);
} else {
System.out.println(searchfor + "not in the array");
}
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}
}
Labeled-Break Example
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Branching #2 : Continue Statement


We use the continue statement to skip the
current iteration of a for, while , or do-while loop.
The unlabeled form skips to the end of the
innermost loop's body and evaluates the boolean
expression that controls the loop, basically
skipping the remainder of this iteration of the
loop.
The following program, ContinueDemo , steps
through a string buffer checking each letter. If
the current character is not a p, the continue
statement skips the rest of the loop and proceeds
to the next character. If it is a p, the program
increments a counter, and converts the p to an
uppercase letter.
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Continue - Example
public class ContinueDemo {
public static void main(String[] args) {
StringBuffer searchMe = new StringBuffer(
"peter piper picked a peck of pickled peppers");
int max = searchMe.length();
int numPs = 0;
for (int i = 0; i < max; i++) {
//interested only in p's
if (searchMe.charAt(i) != 'p')
continue;
//process p's
numPs++;
searchMe.setCharAt(i, 'P');
}
System.out.println("Found " + numPs + " p's in the string.");
System.out.println(searchMe);
}
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Branching #3: Return Statement




The last of Java's branching statements is the return
statement.
We use return to exit from the current method. The flow of
control returns to the statement that follows the original
method call.
The return statement has two forms: one that returns a
value and one that doesn't.
To return a value, simply put the value (or an expression
that calculates the value) after the return keyword:
return value:


The data type of the value returned by return must match
the type of the method's declared return value.
When a method is declared void, use the form of return
that doesn't return a value:
return:
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