9-java language basics part3

LANGUAGE BASICS PART3
JAVA
BY AMR ELGHADBAN

JAVA :Language Basics part3
EXPRESSIONS
▸ the following expression gives different results, depending on
whether you perform the addition or the division operation ﬁrst:
x + y / 100 // ambiguous
▸ to make the previous expression unambiguous, you could write
the following: using balanced parenthesis: ( and ).
(x + y) / 100 // unambiguous, recommended
x + (y / 100) // unambiguous, recommended

BLOCKS
▸ A block is a group of zero or more statements between
balanced braces and can be used anywhere a single
statement is allowed. The following example illustrates the
use of blocks:
class BlockDemo {
public static void main(String[] args) {
boolean condition = true;
if (condition) { // begin block 1
System.out.println("Condition is true.");
} // end block one
else { // begin block 2
System.out.println("Condition is false.");
} // end block 2
}
}

THE IF-THEN AND IF-THEN-ELSE STATEMENTS
▸ The if-then statement is the most basic of all the control ﬂow statements. It
tells your program to execute a certain section of code only if a particular test
evaluates to true:
void applyBrakes() {
// the "if" clause: bicycle must be moving
if (isMoving){
// the "then" clause: decrease current speed
currentSpeed--;
}
}
———————————-
void applyBrakes() {
// same as above, but without braces
if (isMoving)
currentSpeed--;
}
▸ Deciding when to omit the braces is a matter of personal taste.

▸ The if-then-else statement provides a secondary path
of execution when an "if" clause evaluates to false.
void applyBrakes(){  
if (isMoving) {
currentSpeed--;
} else {
System.err.println("The bicycle has already
stopped!");
}
}

class IfElseDemo {
int testscore = 76;
char grade;
if (testscore >= 90) {
grade = 'A';
} else if (testscore >= 80) {
grade = 'B';
grade = 'C';
grade = 'D';
} else {
grade = 'F';
}
System.out.println("Grade = " + grade);
}
}

THE SWITCH STATEMENT
▸ A switch works with the byte, short, char, and int primitive data types.
▸ The body of a switch statement is known as a switch block.
▸ A statement in the switch block can be labeled with one or more case or
default labels.
▸ The switch statement evaluates its expression, then executes all
statements that follow the matching case label.
▸ Another point of interest is the break statement. Each break statement
terminates the enclosing switch statement.
▸ The break statements are necessary because without them, statements in
switch blocks fall through: All statements after the matching case label
are executed in sequence, regardless of the expression of subsequent
case labels, until a break statement is encountered.

▸ public class SwitchDemo {
int month = 8;
String monthString;
switch (month) {
case 1:
monthString = “January";
break;
case 2:
monthString = “February";
break;
case 3:
monthString = “March";
break;

▸ case 4:
monthString = "April";
break;
case 5:
monthString = “May”;
break;
case 6:
monthString = "June";
break;
case 7:
monthString = "July";
break;

case 8:
monthString = "August";
break;
case 9:
monthString = “September";
break;
case 10:
monthString = "October";
break;
case 11:
monthString = "November";
break;

case 12:
monthString = "December";
break;
default:
monthString = "Invalid month";
break;
}
System.out.println(monthString);
}
} // end of class
In this case, August is printed to standard output.

‣ The following code example
shows how a statement can have
multiple case labels.
‣ The code example calculates the
number of days in a particular
month:

class SwitchDemo2 {
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; 
default:  
System.out.println("Invalid month.");  
break; 
}//end of switch block
System.out.println("Number of Days = “ + numDays);  
} // end of main method  
}// end of class

USING STRINGS IN SWITCH STATEMENT.
▸ In Java SE 7 and later, you can use a String object in the
switch statement's expression.
case "january":
monthNumber = 1;
break;
▸ The String in the switch expression is compared with
the expressions associated with each case label as if the
String.equals method were being used.
▸ Note: This example checks if the expression in the switch
statement is null. Ensure that the expression in any
switch statement is not null to prevent a
NullPointerException from being thrown.

THE WHILE AND DO-WHILE STATEMENTS
▸ InThe while statement continually executes a block of
statements while a particular condition is true. Its syntax
can be expressed as:
while (expression) {
statement(s)
}

▸ The while statement evaluates expression, which must
return a boolean value. If the expression evaluates to
true, the while statement executes the statement(s) in
the while block.
▸ The while statement continues testing the expression and
executing its block until the expression evaluates to
false.

▸ Using the while statement to print the values from 1
through 10 can be accomplished as in the following
WhileDemo program:
class WhileDemo {
public static void main(String[] args){
int count = 1;
while (count < 11) {
System.out.println("Count is: " + count);
count++;
}
}
}

▸ You can implement an inﬁnite loop using the while statement as follows:
while (true){
// your code goes here
}
▸ The Java programming language also provides a do-while statement, which
can be expressed as follows:
do {
statement(s)
} while (expression);
‣ The difference between do-while and while is that do-while evaluates its
expression at the bottom of the loop instead of the top. Therefore, the
statements within the do block are always executed at least once.
int count = 12;
do {
System.out.println("Count is: " + count);
count++;
} while (count < 11);

THE FOR STATEMENT “FOR LOOP”
▸ The for statement provides a compact way to iterate over a range of
values.
▸ the way in which it repeatedly loops until a particular condition is
satisﬁed. The general form of the for statement can be expressed as
follows:
for (initialization; termination; increment) {
statement(s)
}
‣ When using this version of the for statement, keep in mind that:
The initialization expression initializes the loop; it's executed once, as the
loop begins.
When the termination expression evaluates to false, the loop terminates.
The increment expression is invoked after each iteration through the loop,
it is perfectly acceptable for this expression to increment or decrement a
value.

THE FOR STATEMENT “FOR LOOP”
▸ Print the numbers 1 through 10 to standard output:
class ForDemo {
public static void main(String[] args){
for(int count=1; count<11; count++){
System.out.println("Count is: " + i);
}
}
}
——————————
‣ // inﬁnite loop
for ( ; ; ) {
// your code goes here
}
——————————
‣ The for statement also has another form designed for iteration
int[] numbers =
{1,2,3,4,5,6,7,8,9,10};
for (int item : numbers){
System.out.println("Count is: " + item);
}

BRANCHING STATEMENTS
▸ The break Statement
▸ You can also use an break to terminate a for, while, or do-while loop
▸ The continue Statement
▸ The continue statement skips the current iteration of a for, while , or do-while loop.
if (searchMe.charAt(i) != ‘p')
continue;
▸ The return Statement
▸ The return statement exits from the current method, and control ﬂow returns to where the
method was invoked.
▸ 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 ++count;
▸ The data type of the returned value 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;

THANKS
WISH YOU A WONDERFUL DAY
▸ Skype : amr_elghadban
▸ Email :amr.elghadban@gmail.com
▸ Phone : (+20)1098558500
▸ Fb/amr.elghadban
▸ Linkedin/amr_elghadban

9-java language basics part3

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9-java language basics part3