02 Core Java IntroTo Language
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Transcript of 02 Core Java IntroTo Language
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An Introduction
Java Technology
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Confidential Mr. Anuj
Agenda
Fundamentals
Operators
Flow Controls
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Java Source File Structure
Java Keywords
Identifiers
Literals
Variables and Data Types
Variable Declaration and Initialization
Operators
Primitive Casting
Flow Controls
Outline
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At the end of this section, you should be able to: Recognize and create correctly constructed source code
Recognize and create correctly constructed declarations
Distinguish between legal and illegal identifiers
Describe all the primitive data types and the ranges ofthe integral data types
Recognize correctly formatted data types
Learn to properly declare and initialize variables
Understand the contents of the argument list of anapplications main() method
Objectives
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Objectives (continued)
Operators: Learn to use: Unary operators
Arithmetic operators
String operators
Relational operators
Conditional operators
Logical operators
Assignment operators
Be familiar with object, shift and bitwise operators
Identify the order of evaluation and change its precedence
Learn how to cast primitive data types
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Objectives (continued)
Flow Controls: Learn syntax and correct use of:
if-else() statement
switch() statement
while() statement
do-while() statement
for() statement
break, continue and label statements
Introduce the concept of return statement
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/** Created on Jul 14, 2005** First Java Program*/
package com.jds.sample;import java.util.*;
/*** @author JDS*/
public class JavaMain {
public static voidmain(String[] args) {// print a messageSystem.out.println("Welcome to Java!");
}}
class Extra {/** class body*/
}
1. Package declaration
Used to organize a collection ofrelated classes.
2. Import statement
Used to reference classes anddeclared in other packages.
3. Class declaration
A Java source file can have several
classes but only one public class is
allowed.
declaration order
Java Source File Structure
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1. Single Line Comment
// insert comments here
2. Block Comment
/*
* insert comments here
*/
3. Documentation Comment
/**
* insert documentation
*/
/** Created on Jul 14, 2005** First Java Program*/
package com.jds.sample;import java.util.*;
/*** @author JDS*/
public class JavaMain {
public static voidmain(String[] args) {// print a messageSystem.out.println("Welcome to Java!");
}}
class Extra {/** class body*/
}
Java Source File Structure
Comments
Tabs and spaces are ignored bythe compiler. Used to improvereadability of code.
Whitespaces
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/** Created on Jul 14, 2005** First Java Program*/
package com.jds.sample;import java.util.*;
/*** @author JDS*/
public class JavaMain {
public static voidmain(String[] args) {// print a messageSystem.out.println("Welcome to Java!");
}}
class Extra {/** class body*/
}
Every java program includes at
least one class definition. Theclass is the fundamentalcomponent of all Java programs.
A class definition contains all thevariables and methods that makethe program work. This is
contained in the class bodyindicated by the opening andclosing braces.
Java Source File Structure
Class
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/** Created on Jul 14, 2005** First Java Program*/
package com.jds.sample;import java.util.*;
/*** @author JDS*/
public class JavaMain {
public static voidmain(String[] args) {// print a messageSystem.out.println("Welcome to Java!");
}}
class Extra {/** class body*/
}
Java Source File Structure
Braces are used for groupingstatements or block of codes.
The left brace ({) indicatesthe beginning of a class body,
which contains any variablesand methods the class needs.
The left brace also indicatesthe beginning of a methodbody.
For every left brace that
opens a class or method youneed a corresponding rightbrace (}) to close the class ormethod.
A right brace always closesits nearest left brace.
Braces
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/** Created on Jul 14, 2005** First Java Program*/
package com.jds.sample;import java.util.*;
/*** @author JDS*/
public class JavaMain {
public static voidmain(String[] args) {// print a messageSystem.out.println("Welcome to Java!");
}
}
class Extra {/** class body*/
}
Java Source File Structure
This line begins the main()
method. This is the line at whichthe program will begin executing.
main() method
Declares a parameter namedargs, which is an array of String.
It represents command-linearguments.
String args[]
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/** Created on Jul 14, 2005** First Java Program*/
package com.jds.sample;import java.util.*;
/*** @author JDS*/
public class JavaMain {
public static voidmain(String[] args) {// print a messageSystem.out.println("Welcome to Java!");
}
}
class Extra {/** class body*/
}
Java Source File Structure
A complete unit of work in aJava program.
A statement is alwaysterminated with a semicolon andmay span multiple lines in yoursource code.
Java statement
Semicolon (;) is the terminating
character for any java statement.
Terminating characterThis line outputs the stringWelcome to Java! followed by
a new line on the screen.
System.out.println()
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true
strictfp
null
implements
extends
char
transient
static
new
if
else
catch
throws
short
native
double
case
throw
return
long
for
do
byte
while
this
public
interface
float
default
break
volatile
synchronized
protected
int
finally
continue
boolean
void
switch
private
instanceof
final
assert
try
super
package
import
false
class
abstract
Java Keywords
gotoconst
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printMeis not the same as PrintMe
Identifiers
An identifieris the name given by aprogrammer to a variable, statementlabel, method, class, and interface
An identifier must begin with a letter,$ or _
Subsequent characters must beletters, numbers, $ or _
An identifier must not be a Javakeyword
Identifiers are case-sensitive
Incorrect Correct
3strikes strikes3Write&Print Write_Print
switch Switch
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A literalis a representation of a value of a particular type
Literals
Type Examples & Values
boolean true false
character a \uFFFF' \777
integer 123 123L O123 Ox123
floating-point 123.5 123.5D 123.5F 123.5e+6
object test null
escape sequences \n \t \b \f \r \ \ \\
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Variable and Data Types
A variableis a named storage location used to representdata that can be changed while the program is running
A data typedetermines the values that a variable cancontain and the operations that can be performed on it
Categories of data types:
1. Primitive data types
2. Reference data types
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What is strongly typed means?
Java is what is known as a strongly typedlanguage.
That means that Java is a language that will only accept specific values
within specific variables or parameters.
Some languages, such as JavaScript, are weakly typed languages. This
means that you can readily store whatever you want into a variable.
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Here is an example of the difference between strongly typedand weakly typed languages:
JavaScript (weakly typed)
1: var x; // Declare a variable
2: x = 1; // Legal
3: x = "Test"; // Legal
4: x = true; // Legal
Java (strongly typed)
1: int x; // Declare a variable of type int
2: x = 1; // Legal
3: x = "Test" // Compiler Error
4: x = true; // Compiler Error
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Primitive Data Types
Type Bits Lowest Value Highest Value
boolean (n/a) false true
char 16 '\u0000' [0] '\uffff' [216-1]
byte 8 -128 [-27] +127 [27-1]
short 16 -32,768 [-215] +32,767 [215-1]
int 32 -2,147,483,648 [-231] +2,147,483,647 [231-1]
long 64 -9,223,372,036,854,775,808 [-263] +9,223,372,036,854,775,807 [263-1]
float 32 1.40129846432481707e-45 3.40282346638528860e+38
double 64 4.94065645841246544e-324 1.79769313486231570e+308
Primitive data types represent atomicvalues and are built-in to Java
Java has 8 primitive data types
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Reference Data Types
Reference data types represent objects
A referenceserves as a handle to the object, it isa way to get to the object
Java has 2 reference data types
1. Class
2. Interface
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Declaring a variable with primitive data type
int age = 21;
Declaring a variable with reference data type
Date now = new Date();
String name =
Jason
;
Variable Declaration & Initialization
identifier
name
primitive
type
initial
value
identifiername
referencetype
initialvalue
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Primitive Type Declaration
Identifiername
type
int age;
stack
age = 17;
valueIdentifiername
age
MEMORY
declaration
initialization/assignment
allot space to memory
017
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The heap
Car object
Values
Reference Type Declaration
type
Car myCar;
myCar = new Car(Bumble Bee);
Identifiername
Bumble Bee
memory address
location
allot space to memory
reference
myCar
Identifiername
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Class Account
int num;
char type;
double balance;
num = 101;
type = S
balance = $1000.00 ;
Account obj1
num = 241;
type = C
balance = $4890.00 ;
Account obj2
Memory
0x 0fed02e
0x 0fc024b
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Member VariablesDeclared inside the classbut outside of all methods.Accessible by all methodsof the class.
Local Variables Availableonly within the methodwhere they were declared.
Method parameters havelocal scope.
Scope of Variable
public class HelloWorld {//accessible throughout the class
String name;
public void otherMethod(){
float salary = 15000.00f;
//cant access age variable from here}
public static void main(String args[ ]) {
//cant access salary variable from here
int age=17;
//cant access ctr variable from herefor (int ctr=0 ; ctr
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Fundamentals
Operators
Flow Controls
Agenda
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Unary operators
Arithmetic operators
String operator
Relational operators
Conditional operator Logical operator
Assignment operators
Object operators
Shift operators
Bitwise operators
Evaluation order
Primitive Casting
Operators and Assignments
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Unary Operators
Unary operators use only one
operand
++ Increment by 1, can be prefix or postfix
-- Decrement by 1, can be prefix or postfix
+ Positive sign
- Negative sign
int num=10;
System.out.println("incrementing/decrementing...");
System.out.println(++num);
System.out.println(--num);System.out.println(num++);
System.out.println(num--);
System.out.println("setting signs...");
System.out.println(+num);
System.out.println(-num);
incrementing/decrementing...
11
10
10
11setting signs...
10
-10
Sample code: Sample output:
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Arithmetic Operators
Arithmetic operators are used for basic
mathematical operations
+ Add
- Subtract
* Multiply
/ Divide
% Modulo, remainder
int num1=15, num2=10;
System.out.println("calculating...");
System.out.println(num1 + num2);
System.out.println(num1 - num2);System.out.println(num1 * num2);
System.out.println(num1 / num2);
System.out.println(num1 % num2);
calculating...
25
5
150
15
Sample code: Sample output:
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String Operator
String operator (+) is used to concatenate operands If one operand is String, the other operands are converted to String
String fname = "Josephine", lname = Luv", mi = "T";
String fullName = lname +", " + fname +" " + mi + ".";
String nickName = "Jessy";
int age=21;
System.out.println("My full name is: "+ fullName);
System.out.println("You can call me "+ nickName +"!");
System.out.println("I'm "+ age +" years old.");
My full name is: Luv, Josephine T.
You can call me Jessy!
I'm 21 years old.
Sample code:
Sample output:
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Relational Operators
Relational operators are used to compare values boolean values cannot be compared with non-boolean values Only object references are checked for equality, and not their states Objects cannot be compared with null null is not the same as
< Less than
Greater than
>= Greater than or equal to
== Equals
!= Not equals
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Relational Operators
String name1 = "Marlon"; int weight1=140, height1=74;
String name2 = "Katie"; int weight2=124, height2=78;
boolean isLight = weight1 < weight2, isLightEq = weight1 height2, isTallEq = height1 >= height2;
System.out.println("Is " + name1 + " taller than " + name2 + "? " + isTall);
System.out.println("Is " + name1 + " taller or same height as " + name2 + "? " + isTallEq);
boolean isWeighEq = weight1 == weight2, isTallNotEq = height1 != height2;
System.out.println("Is " + name1 + " same weight as " + name2 + "? " + isWeighEq);
System.out.println("Is " + name1 + " not as tall as " + name2 + "? " + isTallNotEq);
System.out.println("So who is heavier?");
System.out.println("And who is taller?");
Is Marlon lighter than Katie? false
Is Marlon lighter or same weight as Katie? false
Is Marlon taller than Katie? false
Is Marlon taller or same height as Katie? false
Is Marlon same weight as Katie? false
Is Marlon not as tall as Katie? true
So who is heavier?
And who is taller?
Sample code:
Sample output:
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The ternary operator (?:) provides a handy way to code simple if-else()
statements in a single expression, it is also known as the conditional operator If condition is true, then exp1 is returned as the result of operation
If condition is false, then exp2 is returned as the result of operation
Can be nested to accommodate chain of conditions
Conditional operator
condition ? exp1 : exp2;
int yyyy=1981, mm=10, dd=22;
String mmm = mm==1?"Jan":mm==2?"Feb":mm==3?"Mar":mm==4?"Apr":mm==5?"May":mm==6?"Jun":
mm==7?"Jul":mm==8?"Aug":mm==9?"Sep":mm==10?"Oct":mm==11?"Nov":mm==12?"Dec":"Unknown";
System.out.println("I was born on " + mmm + " " + dd + ", " + yyyy);
I was born on Oct 22, 1981
Sample code:
Sample output:
Syntax:
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Logical Operators
Logical operators are used to compareboolean expressions
! inverts a boolean value & | evaluate both operands && || evaluate operands conditionally
! NOT
& AND
| OR
^ XOR
&& Short-circuit AND
|| Short-circuit OR
Op1 Op2 !Op1 Op1 & Op2 Op1 | Op2 Op1 ^ Op2 Op1 && Op2 Op1 || Op2
false false true false false false false false
false true true false true true false true
true false false false true true false true
true true false true true false true true
Truth Table
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Similar to the Boolean operators, but with an added ability to
short-circuit part of the process, using a couple of mathematicalrules:
If the left operand of an && operation is false, the result isautomatically false, and the right operand is not evaluated
If the left operand of an || operation is true, the result isautomatically true, and the right operand is not evaluated
Boolean Complement ( ! ):
The NOT function inverts the value of boolean
Short-circuit Logical Operators (&&,|| and !)
boolean a = (5>8) && (8>5);false;
boolean b = (8>5) || (5>8);true;
boolean c = !b;false;
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Logical Operators
int yrsService=8;
double perfRate=86;
double salary=23000;
char position='S';
// P-probationary R-regular, S-supervisor, M-manager, E-executive, T-top executive
boolean forRegular, forSupervisor, forManager, forExecutive, forTopExecutive;
forRegular = yrsService>1 & perfRate>80 & position=='P'& salary5 & perfRate>85 & position=='R'& salary7 & perfRate>85 & position=='S'& salary10 & perfRate>80 & position=='M'& salary10 & perfRate>80 & position=='E'& salary
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Assignment Operators
Assignment operators areused to set the value of avariable
= Assign
+= Add and assign
-= Subtract and assign
*= Multiply and assign
/= Divide and assign
%= Modulo and assign
&= AND and assign
|= OR and assign
^= XOR and assign
double unitPrice=120, qty=2, salesAmount;double discRate=15, discAmount, vatRate=10, vatAmount;
// compute gross sales
salesAmount = unitPrice * qty;
System.out.println("Gross Sales: " + salesAmount);
// compute tax
vatRate /= 100;vatAmount = salesAmount * vatRate;
salesAmount += vatAmount;
System.out.println("Tax: " + vatAmount);
// compute discount
discRate /= 100;
discAmount = salesAmount * discRate;
salesAmount -= discAmount;
System.out.println("Discount: " + discAmount);
System.out.println("Please pay: " + salesAmount);
Gross Sales: 240.0
Tax: 24.0
Discount: 39.6
Please pay: 224.4
Sample code:
Sample output:
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Casting
Castingis converting from one data type to another
Implicit castingis an implied casting operations
Explicit castingis a required casting operations
Primitive castingis converting a primitive data type to another
Widening conversionis casting a narrower data type to a broader
data type Narrowing conversionis casting a broader data type to a narrower
data type
Reference castingis converting a reference data type to another
Upcastingis conversion up the inheritance hierarchy
Downcastingis conversion down the inheritance hierarchy Casting between primitive and reference type is not allowed
In Java, casting is implemented using () operator
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Primitive Casting Flow
byte short int long float double
char
widening conversion
narrowing conversion
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Primitive Casting Rule
arithmetic implicit widening conversion
relational implicit widening conversion
shift implicit widening conversion
bitwise implicit widening conversion
assignment implicit widening conversion (if target is broader )
parameter passing implicit widening conversion (if formal parameter is broader)
logical none
ternary ?: noneboolean none
(all others) explicit casting (narrowing or widening conversion)
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Implementing Primitive Casting
public static voidmain(String args[]) {short age = 20;char sex = M;byte iq = 80;int height = 64;long distance =300;float price = 99.99f;
double money = 500.00;
age = sex; // will this compile?sex = iq; // will this compile?iq = (byte) height; // will this compile?distance = height; // will this compile?
price = money; // will this compile?sex = (char) money; // will this compile?
}
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Evaluation order of operators in Java is as follows:
Unary (++ -- + - ~ ())
Arithmetic (* / % + -)
Shift (> >>>) Comparison (< >= instanceof == !=)
Bitwise (& ^ |)
Short-circuit (&& || !)
Conditional (?:) Assignment (= += -= *= /=)
Summary of Operators
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Fundamentals Operators
Flow Controls
Agenda
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Flow Controls
if-else() statement
switch() statement
while() statement
do-while() statement
for() statement
break statement
continue statement
Statement label
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Types of Flow Control
1. Sequential Perform statements in the order
they are written
1. Selection Perform statements based on
condition
1. Iteration Perform statements repeatedly
based on condition
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if-else() Construct
if-else() performs statements based on two conditions Condition should result to a boolean expression If condition is true, the statements following if are executed If condition is false, the statements following else are executed
Can be nested to allow more conditions
if (condition) { // braces optional
// statement required
}
else { // else clause is optional
// statement required
}
int age=10;
if (age < 10) {
System.out.println("You're just a kid.");
} else if (age < 20){System.out.println("You're a teenager.");
} else {
System.out.println("You're probably old...");
}
Syntax:
Example:
You're a teenager.Output:
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switch() construct
switch() performs statements based on multiple conditions exp can only be char byte short int, val should be a unique constant of exp
case statements falls through the next case unless a break is encountered default is executed if none of the other cases match the exp
switch (exp) {
caseval:
// statements here
caseval:
// statements here
default:
// statements here
}
char sex='M';
switch (sex){
case'M':
System.out.println("I'm a male.");break;case'F':
System.out.println("I'm a female.");break;
default:
System.out.println("I am what I am!");
}
Syntax:
Example:
I'm a male.Output:
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while() loop
while() performs statements repeatedly whilecondition
remains truewhile (condition) { // braces optional
// statements here
}
int ctr=10;
while (ctr > 0) {System.out.println("Timer: " + ctr--);
}
Syntax:
Example:
Timer: 10
Timer: 9
Timer: 8
Timer: 7Timer: 6
Timer: 5
Timer: 4
Timer: 3
Timer: 2
Timer: 1
Output:
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do-while() loop
do-while() performs statements repeatedly (at least once) while
conditionremains truedo
// statements here
while (condition);
int ctr=0;
do
System.out.println("Timer: " + ctr++);
while (ctr < 10);
// next statement
Syntax:
Example:
Timer: 0
Timer: 1
Timer: 2
Timer: 3Timer: 4
Timer: 5
Timer: 6
Timer: 7
Timer: 8
Timer: 9
Output:
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for() loop
for() performs statements repeatedly based on a condition
Init is a list of either declarations or expressions, evaluated firstand only once Conditionis evaluated beforeeach iteration
Expis a list of expressions, evaluated aftereach iteration
All entries inside () are optional, for(;;) is an infinite loop
for (init; condition; exp) { // braces optional
// statements here
}
for (int age=18; age
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break
break exits loops and switch() statements
break;
boolean isEating=true;
int moreFood=5;
while (isEating) {
if (moreFood
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continue
continue is used inside loops to start a new iteration
continue;
for (int time=7; time
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Statement Label A label is an identifier placed before a statement, it ends with : break labelNameis used to exit any labelled statement
continue labelName is used inside loops to start a new iteration of the labeled loop
labelName:
break labelName;
continue labelName;
int[] scores = {3,9,10,0,8,10,7,1,9,8};
outer:
for (int i=0; i
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Example 1:
public int sum(int x, int y) {return x + y;
}
Example 2:
public int sum(int x, int y) {
x = x + y;
if (x < 100){return x;
}else{
return x + 5;
}
}
Example 2:public void getSum(int x) {
System.out.println(x);
return;
}
return branchingstatement is used toexit from the currentmethod.
Two forms:
return ; return;
return
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Key Points
A Java source file can include package, import and class
declarations in that order The main() method is the start of execution of a Java
application
Each Java statement is terminated by a semicolon ;
Identifiers are case-sensitive Java keywords cannot be used as identifiers
Each variable must be declared with a data type
There are 8 primitive data types: boolean, char, byte,
short, int, long, float and double There are 3 reference data types: class, array and
interface
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Key Points (continued)
Use unary, arithmetic operators for basic mathematical
operations
Use string operator to concatenate strings
Use relational operators to compare objects
Use conditional operator as alternative to if-else()
statement
Use logical operators to compare boolean values
Use assignment operators to assign values to variables
Get familiar with object, shift and bitwise operators Java evaluates operators in order of precedence
Castingis converting one data type to another
Ke Points
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Key Points
if() and switch() are used for branching statements
while(), do-while() and for() are used for iterating
statements
break, continue and labelare used to branch inside
loops
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http://www.java.sun.com
http://www.java.com
http://www.java.net
http://javaboutique.internet.com
http://javaboutique.webdeveloper.com
http://www.javaworld.com http://www.developer.com
http://javalobby.org
http://freewarejava.com
http://onjava.com
http://javaranch.com http://www.cafeaulait.org
http://www.java.about.com
http://www.javacoffeebreak.com
Java Online Resources
http://www.java.sun.com/http://www.java.com/http://www.java.net/http://javaboutique.internet.com/http://javaboutique.webdeveloper.com/http://www.javaworld.com/http://www.developer.com/http://javalobby.org/http://freewarejava.com/http://onjava.com/http://onjava.com/http://onjava.com/http://freewarejava.com/http://freewarejava.com/http://javalobby.org/http://javalobby.org/http://www.developer.com/http://www.developer.com/http://www.javaworld.com/http://www.javaworld.com/http://javaboutique.webdeveloper.com/http://javaboutique.webdeveloper.com/http://javaboutique.internet.com/http://javaboutique.internet.com/http://www.java.net/http://www.java.com/http://www.java.com/http://www.java.sun.com/http://www.java.sun.com/ -
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Tutorials:
http://java.sun.com/docs/books/tutorial http://www.ibiblio.org/javafaq/javatutorial.html
http://www.javacoffeebreak.com/tutorials/index.html http://www.cafeaulait.org/course/ http://oopweb.com/Java/Documents/IntroToProgrammingUsingJav
a/VolumeFrames.html
FAQs: http://java.sun.com/products/jdk/faq.html
http://www.ibiblio.org/javafaq/javafaq.html http://www.apl.jhu.edu/~hall/java/Beginners-Corner.html http://www.norvig.com/java-iaq.html http://www.jguru.com/faq/subtopics.jsp?topic=JavaLanguage http://www.javacoffeebreak.com/faq/
Java Online Resources
Q i d C
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Questions and Comments