Java - Trang ď Chap03-04

Programming Java

Control Statements

Incheon Paik

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Java

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Contents
„
„
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„
„
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„
„
„

Java

The if Statement and if-else Statement
Blocks of Code
The For Statement
The While Loop and Do-While Loop

The Break, Continue, and Switch Statements
Increment Operator & Decrement Operator
Back-slash codes
Relational and Boolean Logical Operators
Three Terms Operator
Bit Operators
The Assertion Statement

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Control Statements
„
„

To change the execution order of program
As the method of controlling the execution order
„
„
„

Conditional Statement : if St., switch St.
Repeat Statement : for St., while St., do-while St.
Branch Statement : break St., continue St., return St.

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The If Statement and If – else Statement
„

Form of the if Statement
„ if ( <conditional expression> ) <statement>
„ if ( < conditional expression > ) <statement1>
else <statement2>
„

Result of conditional expression

:

Logical

Type(true or false)

Java

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The If and If-Else Statement
„

Nested if statement
if (<cond. expr.>)
if (<cond. expr.>)
// . . .
<statement>
if (<cond. expr.1>)
<statement 1>
else if (<cond. expr.2>) < statement 2>
…
else if (<cond. expr. n>) < statement n>
else < statement>

„

A Block of
Code

if (expression) {
statement1;
statement2;
………….
}
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The For Statement
„

„

Repeat the sequence of statements as many as defined.
Form of the for statement
for ( <expr. 1> ; < expr. 2> ; < expr. 3>)
<statement>
„
„
„

<expr. 1> : initialize the control variable
<expr. 2> : check the control variable
<expr. 3> : modify the control variable

s = 0;
for (i=1; i<=N; ++i)
s += i;

Java

// sum from 1 to N : i increment

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The For Statement
„

Execution order of the for statement

1

5

2

for ( < Expr1>;<
Expr3>)
Expr1>;<Expr2> ; <Expr3>

3
6

4

>

False

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The Collection-based For Loop
This expression specified the variable, season,

of type Season in this case, that will be assigned
each of the values in the collection in turn.
This expression identifies the collection that is
the source of data values to be iterated over.
In this case it is all the values in the enumeration
Season.
for ( Season season : Season.values() ) {
System.out.println (“The season is now “ + season);
}

// <statement>

A colon separates the two control expressions
in this type of for loop

Java

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The Repeat Statement - while Statement
„

Form of the while statement
while ( cond. Expr. )
<Statement>

„

Order of Execution

i = 1; s = 0;
while (i <= N) { // summation from 1 to N
s += i; ++i;
}

(1)
while (< Cond.
Cond. Expr.
Expr.>)

(4)
False

(2) True

(3)

< Statement >
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The Repeat Statement - while Statement

„

Comparison of the for statement and the while statement

i = 0;
while (i < N) {
s += i;
++i;
}

for (i = 0; i < N; ++i)
s += i;

Java

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The Repeat Statement – do - while Statement

After executing the repeating statements, then check the conditional
expression
Form of the do-while statement

„

„

Although

Althoughthe
theconditional
conditionalexpression
expression

do
<statement>
while (<conditional expression>);

isisfalse,
false,execute
executethe
thestatement
statement
one
time
above
one time aboveatatleast
least

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The Branch Statement - break Statement

„
„

To move control to the out of the block
From of the break statement
break [label] ;

int i = 1;
while (true) {
if (i == 3)
break;
System.out.println("This is a " + i + " iteration");
++i;
}

Java

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The Branch Statement - break Statement

„

Label the break statement
„ Can be used instead of goto statement
„ Form of usage
labelName :
Rep. St. 1 {
Rep. St. 2 {

// . . .
break;
// . . .
break labelName;
labelName;
}
// . . .
}

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The Branch Statement – continue Statement

„

To move control to the start of next repeatation

„

From of the continue statement
continue [Label] ;

„

When used in the for statement

for (i=0; i<=5; ++i) {
if (i % 2 == 0)
continue;
System.out.println("This is a " + i + " iteration");
}

Java

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The Branch Statement – continue Statement

„

When used in the while statement

i = 0;
while (i <= 5) {
++i;
if (i % 2) == 0)
continue;
System.out.println("This is a odd iteration - " + i);
}

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The Branch Statement – continue Statement

„

Label the continue statement
labelName:
labelName:
Rep. St. 1 {
Rep. St. 2 {
// ...
continue;
// ...
continue labelName;
labelName;

}
}

Java

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The Branch Statement – return Statement

„

„

To terminate the execution of method, then pass the method of
caller that control
Forms of the return statement
„
„

return;
return .>;
<expr.>;
a]

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Increment & Decrement Operator
„

Operator
„ ++, -„ Prefix operator
nn==1;1;
xx==++n;
++n;

„

Postfix operator
nn==1;1;
xx==n++;
n++;

„
„

Java

////x=2,
x=2,n=2
n=2

////x=1,
x=1,n=2
n=2

Cannot be use with expressions, only with variables
Cannot be applied at the real type (a + b)++ // error
(a + b)++

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// error

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Back-Slash Codes
class SpecialCharacters {

¥b back space

public static void main(String args[]) {

¥n new line

System.out.print(“¥u00a0 ¥u00a1
¥u00a2 ¥u00a3”);

¥r carrage return

}

¥f form feed
¥t

}

tab

¥” double quotation
¥’ single quotation
¥0 null
¥¥ back slash
¥uxxxx Unicode (x: hexa decimal)

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Bitwise Operators
„

Operator
„
&, |, <<, >>, >>>, ^, ~
„ Operand should be integer type
„
Precedence

Operator
~
<< >> >>>
&
^
|

Java

Precedence
(H)

(L)

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Bitwise Operators
„

„

„

„

Bitwise AND
„ 10012 & 00112 = 00012
„ To extract the special area in variable by masking that area
Bit OR
„ 10012 | 00112 = 10112
Exclusive OR
„ 10012 ^ 00112 = 10102
1’s Complement
„ ~ 000010102 = 111101012

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Java

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Bitwise Operators
„

Bitwise Shift Operator
„

Shift lefe(<<)
y
xx<<
<
„

Shift right(>>)
y
xx>>
>>yy==xx//22y

„

Unsigned shift right(>>>)
„

Java

Give this operator because Java does not support unsigned
integer.
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Comparing enumeration values
Definition of enumeration type
enum
enumSeason
Season{spring,
{spring,summer,
summer,fall,
fall,winter}
winter}

Check the value
Season
Seasonseason
season==Season.summer;
Season.summer;
if(Season.equals(Season.spring)
if(Season.equals(Season.spring){{
System.out.println(“Spring
System.out.println(“Springhas
hassprung,
sprung,the
thegrass
grassisisriz.”);
riz.”);
}}else
{
else {
System.out.println(“It

System.out.println(“Itisn¥’
isn¥’Spring”);
Spring”);
}}
****Sample
SampleCode
Code::

/> />
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Ternary Operator
„

Operator
„
Expr1 ? Expr2 : Expr3 (3 Terms Operator)
if (x > y) max = x;
else max = y;

max
max==xx>>yy??xx::yy;;

mm==aa>>bb??(c(c>>aa??cc::a)a)::(c(c>>bb??cc::b)
b);;

Java

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Assignment Operators
Expr1
Expr1 op=
op= Expr
Expr22

Expr
Expr11==Expr
Expr11 op
opExpr2
Expr2
„

Operator
„ Arithmetic operator : + - * / %
„ Bitwise operator : & | ^ << >> >>>

sum
sum==sum
sum++ii;;

sum
sum+=

+= ii;;

xx==xx*
*yy++1;1;

xx*=
*=yy++1;1;

x = x * (y+1)
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Cast Operators
„

Data Type Casting Operator

(Data
Type)
Expression
(Data
Type)
Expression
„ Cast
operator
:(, )
(int)

(int)3.75
3.75
(float)
(float)33
(float)
(float)(1
(1//2)
2)
(float)1/2
(float)1/2

Java

===>
===>
===>
===>
===>
===>
===>
===>

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3.0
3.0
0.0
0.0
0.5
0.5

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Operator Precedence
Operator

Association

() [] .
! ~ ++ -- + - (Data Type)
* / %
+ << >> >>>
< <= > >= instance
== !=
&
^
|
&&
||
?:
= += -= *= /= %= &= ^= |= <<= >>= >>>=

Left Assoc.
Right Assoc.
Left Assoc.
Left Assoc.
Left Assoc.
Left Assoc.

Left Assoc.
Left Assoc.
Left Assoc.
Left Assoc.
Left Assoc.
Left Assoc.
Right Assoc.
Right Assoc.
(Low)

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Java

Precedence
(High)

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Operator Precedence
„

„
„
„
„

Java

a=x+y-z;

b = -x ;
c = -x++ ;
d = -++x ;
e = -x + z ;

// Left Association
// Right Association

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The Assertion Statements
assert logical_expression;
„

„

„

The assert is a keyword, and a logical_expression is any expre- ssion
that results in a value of true or false.
If logical_expression evaluates to true, then the program continues n
ormally. If logical_expression evaluates to false, the program will
be terminated with an error mess-age starting with:
java.lang.AssertionError
Sample Code “TryAssertions.java”

/>

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Exercise
„

Step 1 , 2
„

„

Step 3 Magic Square

Start

Java

You can try by yourself.

blank

8

blank

blocked

1

6

blank

3

5

7

blank

4

9

2

blocked

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Principle
1.

Basically go right up
direction

2.

If blank, then go to
opposite block

3.

If blocked, go down

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Exercise
„

Step 4
„

Java

Refer to Slides #8, #23.

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