Session 2 Session 2 Java Language Fundamentals 9:17 AM.
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Transcript of Session 2 Session 2 Java Language Fundamentals 9:17 AM.
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Session 2Session 2
Java Language Fundamentals
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ReviewReview
Java was introduced by Sun Microsystems in 1995. Java is a programming language popularly used to build programs that can
work on the Net. Its primary features are: it is object-oriented and a cross platform language. Swing, Drag and Drop, Java 2D API, Java Sound and RMI are some of the
features added to the existing version of Java. A Java applet is designed to work in a pre-defined “sandbox” only. This
makes it safe to be used on the Internet. Java bytecodes are machine language instructions understood by the Java
Virtual Machine and usually generated as a result of compiling Java language source code.
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Review Contd…Review Contd…
Java programs can be divided into following categories-applets, applications, GUI applications, servlets and database applications.
Java visual development tools help the programmer to develop Java applications and applets more quickly and efficiently.
The JDK contains the software and tools needed to compile, debug and execute applets and applications written in the Java language. It’s basically a set of command-line tools.
Enhancement in Swing, AWT, a new I/O class and so on has been added in the latest version of Java 1.4.2.
The future will use a lot of Java related programs for consumer gadgets with embedded technologies.
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ObjectivesObjectives
Interpret the Java ProgramUnderstand the basics of Java Language Identify the Data TypesUnderstand arrays Identify the OperatorsFormat output using Escape Sequence
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A Sample Java A Sample Java programprogram
// This is a simple program called First.javaclass First{ public static void main (String [] args) { System.out.println ("My first program in Java ");
}}
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Analyzing the Java Analyzing the Java Program Program
The symbol // stands for commented line. When longer comments are needed, mark each line with a //.
◦ Or use the /* and */ comment delimiters -> block off a longer comment
The line class First declares a new class called First. public static void main (String [] args)
◦ This is the main method from where the program begins its execution.
System.out.println (“My first program in java”);◦ object.method(parameters)
◦ This line displays the string My first program in java on the screen.
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Phase 1: Creating a Phase 1: Creating a ProgramProgramconsists of editing a file with an editor program
(normally known simply as an editor).A file name ending with the .java extension
indicates that the file contains Java source code. ◦ Eclipse (www.eclipse.org), ◦ NetBeans (www.netbeans.org),◦ JBuilder (www.borland.com), ◦ JCreator (www.jcreator.com), ◦ BlueJ (www.blueJ.org), ◦ jGRASP (www.jgrasp.org) ◦ jEdit (www.jedit.org).
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Phase 2: Compiling a Java Program into Phase 2: Compiling a Java Program into BytecodesBytecodes the programmer uses the command javac (the Java compiler) to compile a program. For
example, to compile a program called Welcome.java, you would type
javac Welcome.java
If the program compiles, the compiler produces a .class file called Welcome.class that
contains the compiled version of the program.
The Java compiler translates Java source code into bytecodes that represent the tasks to
execute in the execution phase (Phase 5). Bytecodes are executed by the Java Virtual
Machine (JVM)—a part of the JDK and the foundation of the Java platform.
A virtual machine (VM) is a software application that simulates a computer, but
hides the under- lying operating system and hardware from the programs that interact
with the VM.
the same VM is implemented on many computer platforms, applications that it executes can be used
on all those platforms.
bytecodes are platform-independent instructions—they are not dependent on a particular
hardware platform (>< machine codes).
->So Java’s bytecodes are portable—that is, the same bytecodes can execute on any
platform containing a JVM that understands the version of Java in which the bytecodes
were compiled.
The JVM is invoked by the java command.
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Phase 3: Loading a Program into Phase 3: Loading a Program into MemoryMemory the program must be placed in memory before it can execute
—known as loading.
java Welcome
The class loader takes the .class files containing the
program’s bytecodes and transfers them to primary memory.
The class loader also loads any of the .class files provided by
Java that your program uses.
The .class files can be loaded from a disk on your system or
over a network (e.g., your local college or company network,
or the Internet).
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Phase 4: Bytecode Phase 4: Bytecode VerificationVerificationas the classes are loaded, the bytecode
verifier examines their bytecodes to ensure that they are valid and do not violate Java’s security restrictions.
Java enforces strong security, to make sure that Java programs arriving over the network do not damage your files or your system (as computer viruses and worms might).
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Phase 5: ExecutionPhase 5: Execution the JVM executes the program’s bytecodes, thus performing the
actions specified by the program.
In early Java versions, the JVM was simply an interpreter for Java
bytecodes -> execute slowly. Today’s JVMs typically execute
bytecodes using a combination of interpretation and so-called just-in-
time (JIT) compilation.
Thus Java programs actually go through two compilation phases—
one in which source code is translated into bytecodes (for portability
across JVMs on different computer platforms) and a second in which,
during execution, the bytecodes are translated into machine language
for the actual computer on which the program executes.
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Compiling and executing the Compiling and executing the Java programJava program
The java compiler creates a file called 'First.class' that contains the byte codes
To actually run the program, a java interpreter called java is required to execute the code.
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Passing Command Line Passing Command Line ArgumentsArguments
class CommLineArg{
public static void main (String [] pargs){
System.out.println("These are the arguments passed to the main method.");
System.out.println(pargs [0]);System.out.println(pargs [1]);System.out.println(pargs [2]);
}}
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Passing Command Line Passing Command Line ArgumentsArguments
Output
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Basics of the Java Basics of the Java Language Language
Classes & Methods
Data types
Variables
Constants
Operators
Control structures
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Classes in Java Classes in Java
Class declaration Syntax
class Classname {
var_datatype variablename;:
met_datatype methodname(parameter_list):
}
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Sample classSample class
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Data Types Data Types
byte char boolean short int long float double
Array
Class
Interface
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Integer TypesInteger TypesThe integer types are for numbers without
fractional parts. Negative values are allowed.
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Floating-Point TypesFloating-Point TypesThe floating-point types denote numbers
with fractional parts
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The char TypeThe char Type•The char type is used to describe individual characters.
•For example, 'A' is a character constant with value 65.
•It is different from "A", a string containing a single character. Unicode code units can be
expressed as hexadecimal values that run from \u0000 to \uFFFF.
• For example, \u2122 is the trademark symbol (™) and \u03C0 is the Greek letter pi (π).
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The boolean TypeThe boolean Type The boolean type has two values, false and true. It is used for
evaluating logical conditions.
You cannot convert between integers and boolean values.
void bubbleSort(int[] x, int n) { boolean anotherPass; // true if something was out of order
do { anotherPass = false; // assume everything sorted for (int i=0; i<n-1; i++) { if (x[i] > x[i+1]) { int temp = x[i]; x[i] = x[i+1]; x[i+1] = temp; //
exchange anotherPass = true; // something wasn't sorted, keep going
} } } while (anotherPass);
}
void bubbleSort(int[] x, int n) { boolean anotherPass; // true if something was out of order
do { anotherPass = false; // assume everything sorted for (int i=0; i<n-1; i++) { if (x[i] > x[i+1]) { int temp = x[i]; x[i] = x[i+1]; x[i+1] = temp; //
exchange anotherPass = true; // something wasn't sorted, keep going
} } } while (anotherPass);
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Type CastingType Casting
In type casting, a data type is converted into another data type.
Example float c = 34.89675f;
int b = (int)c + 10;
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Automatic type and Automatic type and CastingCasting
There are two type of data conversion: automatic type
conversion and casting.
When one type of data is assigned to a variable of another
type then automatic type conversion takes place provided
it meets the conditions specified:
◦ The two types are compatible
◦ The destination type is larger than the source type.
Casting is used for explicit type conversion. It loses
information above the magnitude of the value being
converted.
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Type Promotion RulesType Promotion Rules
All byte and short values are promoted to int type.
If one operand is long, the whole expression is promoted to long.
If one operand is float then the whole expression is promoted to float.
If one operand is double then the whole expression is promoted to double.
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VariablesVariablesThree components of a variable
declaration are:◦ Data type
◦ Name
◦ Initial value to be assigned (optional)
Syntaxdatatype identifier [=value][,
identifier[=value]...];
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Initializing VariablesInitializing Variables you must explicitly initialize it by means of an assignment
statement—you can never use the values of uninitialized variables.
the Java compiler flags the following sequence of statements as an
error:
int vacationDays;
System.out.println(vacationDays); // ERROR--variable not initialized
in Java you can put declarations anywhere in your code.
double salary = 65000.0;
System.out.println(salary);
int vacationDays = 12; // ok to declare a variable here
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ExampleExample
Output
class DynVar{
public static void main(String [] args){
double len = 5.0, wide = 7.0;double num = Math.sqrt(len * len + wide * wide);System.out.println("Value of num after dynamic
initialization is " + num);}
}
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Scope and Lifetime of Scope and Lifetime of VariablesVariables
Variables can be declared inside a block. The block begins with an opening curly brace
and ends with a closing curly brace.A block defines a scope. A new scope is created every time a new
block is created. Scope specifies what objects are visible to
other parts of the program.It also determines the life of an object.
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ExampleExampleclass ScopeVar{public static void main(String [] args){int num = 10;if ( num == 10){
// num is available in inner scopeint num1 = num * num;
System.out.println("Value of num and num1 are " + num + " " + num1);
}//num1 = 10; System.out.println("Value of num is " + num);
}}
Output
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ConstantsConstants use the keyword final to denote a constant.
public class Constants
{
public static void main(String[] args)
{
final double CM_PER_INCH = 2.54;
double paperWidth = 8.5;
double paperHeight = 11;
System.out.println("Paper size in centimeters: "
+ paperWidth * CM_PER_INCH + " by " + paperHeight * CM_PER_INCH);
}
} The keyword final indicates that you can assign to the variable once, and then its
value is set once and for all. It is customary to name constants in all uppercase.
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ConstantsConstants It is probably more common in
Java to want a constant that is
available to multiple methods
inside a single class. These are
usually called class constants.
You set up a class constant with
the keywords static final.
Note that the definition of the
class constant appears outside
the main method. Thus, the
constant can also be used in
other methods of the same
class.
public class Constants2
{
public static void main(String[] args)
{
double paperWidth = 8.5;
double paperHeight = 11;
System.out.println("Paper size in
centimeters: “ + paperWidth *
CM_PER_INCH + " by " + paperHeight *
CM_PER_INCH);
}
public static final double CM_PER_INCH =
2.54;
}
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Array DeclarationsArray Declarations
Three ways to declare an array are:
◦datatype identifier [ ];
◦datatype identifier [ ] = new datatype[size];
◦datatype identifier [ ] = {value1,value2,….valueN};
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Example – One Dimensional Example – One Dimensional ArrayArray
class ArrDemo{public static void main(String [] arg){double nums[] = {10.1, 11.3, 12.5,13.7, 14.9};System.out.println(" The value at location 3 is : " +
nums[3]);}
}
Output
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Example – Multi Example – Multi Dimensional ArrayDimensional Arrayclass MultiArrayDemo
{public static void main ( String [] arg){
int multi[][] = new int [4][];multi[0] = new int[4];multi[1] = new int[4];multi[2] = new int[4];multi[3] = new int[4];int num = 0;for (int count = 0; count < 4; count++){
for (int ctr = 0; ctr < count+1; ctr++)
{multi[count][ctr] =
num;num++;
}}
for (int count = 0; count < 4; count++)
{for (int ctr = 0; ctr < count+1;
ctr++){
System.out.print(multi[count][ctr] + " ");
System.out.println();}
}}
}Output
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Operators Operators
Arithmetic Operators
Bitwise Operators
Relational Operators
Logical Operators
Conditional Operators
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Arithmetic OperatorsArithmetic Operators
Operands of the arithmetic operators must be of numeric type.
Boolean operands cannot be used, but character operands are allowed.
These operators are used in mathematical expressions.
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ExampleExampleclass ArithmeticOp{
public static void main ( String [] arg){
int num = 5, num1 = 12, num2 = 20, result;result = num + num1;System.out.println("Sum of num and num1 is : (num + num1) " +
result);result = num % num1;System.out.println("Modulus of num and num1 is : (num % num1) " +
result);result *= num2;System.out.println("Product of result and num2 is : (result *=
num2) " + result);System.out.println("Value of num before the operation is : " + num);
num ++;System.out.println("Value of num after ++ operation is : " + num);double num3 = 25.75, num4 = 14.25, res;res = num3 - num4;System.out.println("num3 – num4 is : " +res);res -= 2.50;System.out.println("res -= 2.50 " + res);System.out.println("Value of res before -- operation is : "+ res);res--;System.out.println("Value of res after -- operation is : " + res);
}}
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Output
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Bitwise OperatorsBitwise Operators
A bitwise operator allows manipulation of
individual bits in an integral primitive data type.
These operators act upon the individual bits of their
operands.
Bitwise operators perform Boolean algebra on the
corresponding bits in the two arguments to produce
the result.
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The bitwise operators are
& (“and”) | (“or”) ^ (“xor”) ~ (“not”) These operators work on bit patterns. For example, if n is an integer
variable, then
int fourthBitFromRight = (n & 8) / 8; gives you a 1 if the fourth bit from the right in the binary representation of
n is 1, and 0 if not. Using & with the appropriate power of 2 lets you mask out all but a single
bit.
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Relational OperatorsRelational Operators
Relational operators test the relation
between two operands.
The result of an expression in which
relational operators are used, is Boolean
(either true or false).
Relational operators are used in control
structures.
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ExampleExampleclass RelOp{
public static void main(String [] args){
float num = 10.0F;double num1 = 10.0;if (num == num1)
System.out.println ("num is equal to num1");else
System.out.println ("num is not equal to num1");}
}
Output
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Logical OperatorsLogical OperatorsLogical operators work with Boolean
operands. Some operators are
◦&◦ |◦^◦!
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Conditional OperatorsConditional OperatorsThe conditional operator is unique, because it is a ternary
or triadic operator that has three operands to the expression.
It can replace certain types of if-then-else statements. The code below checks whether a commuter’s age is
greater than 65 and print the message.
CommuterCategory = (CommuterAge > 65)? “Senior Citizen” : “Regular”;
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Assignment OperatorsAssignment Operators
The assignment operator is a single equal sign, =, and assigns a value to a variable.
Assigning values to more than one variable can be done at a time.
In other words, it allows us to create a chain of assignments.
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Operator Precedence Operator Precedence
Parentheses: ( ) and [ ] Unary Operators: +, -, ++, --, ~, !Arithmetic and Shift operators: *, /, %, +, -, >>, <<Relational Operators: >, >=, <, <=, ==, !=Logical and Bitwise Operators: &, ^, |, &&, ||, Conditional and Assignment Operators: ?=, =, *=, /=, +=, -
=Parentheses are used to change the order in which an
expression is evaluated. Any part of an expression enclosed in parentheses is evaluated first.
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Mathematical Functions and Mathematical Functions and ConstantsConstants The Math class contains an assortment of mathematical functions that you
may occasionally need, depending on the kind of programming that you do.
To take the square root of a number, use the sqrt method:
double x = 4;
double y = Math.sqrt(x);
System.out.println(y); // prints 2.0
The Java programming language has no operator for raising a quantity to a
power. You must use the pow method in the Math class.
double y = Math.pow(x, a);
Math.PI
Math.E
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Formatting output with Escape Formatting output with Escape Sequences Sequences Whenever an output is to be displayed on
the screen, it needs to be formatted. The formatting can be done with the help of
escape sequences that Java provides.System.out.println (“Happy \tBirthday”);
◦Output: Happy Birthday
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Control FlowControl Flow All application development environments provide a decision
making process called control flow statements that direct the
application execution.
Flow control enables a developer to create an application that can
examine the existing conditions, and decide a suitable course of
action.
Loops or iteration are an important programming construct that can
be used to repeatedly execute a set of actions.
Jump statements allow the program to execute in a non-linear
fashion.
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Control Flow Structures in Control Flow Structures in JavaJava
Decision-making◦if-else statement◦switch-case statement
Loops◦while loop◦do-while loop◦for loop
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if-else statementif-else statement The if-else statement tests the result of a condition, and performs
appropriate actions based on the result.
It can be used to route program execution through two different paths.
The format of an if-else statement is very simple and is given below:
if (condition)
{
action1;
}
else
{
action2;
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ExampleExampleclass CheckNum{public static void main(String [] args){int num = 10;if (num % 2 == 0)System.out.println(num + " is an even number");
elseSystem.out.println(num + " is an odd number");
}}
Output
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switch – case statementswitch – case statementThe switch – case statement can be used in
place of if-else-if statement.
It is used in situations where the expression
being evaluated results in multiple values.
The use of the switch-case statement
leads to simpler code, and better
performance.
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ExampleExampleclass SwitchDemo{
public static void main(String[] args){
int day = 4;String str;switch (day){
case 0: str = "Sunday";break;
case 1: str = "Monday"; break;
case 2: str = "Tuesday"; break;
case 3: str =
"Wednesday"; break;
case 4: str = "Thursday"; break;
case 5: str =
"Friday";
break;case 6:
str = "Saturday";
break;
default: str = "Invalid
day"; }
System.out.println(str);}
}Output
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while Loopwhile Loop while loops are used for situations when a loop has to be executed as
long as certain condition is True.
The number of times a loop is to be executed is not pre-determined, but
depends on the condition.
The syntax is:
while (condition)
{
action statements;
.
.
.
}
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ExampleExampleclass FactDemo{public static void main(String [] args){int num = 5, fact = 1;while (num >= 1){
fact *= num; num--;}System.out.println("The factorial of 5 is : " + fact);
}}
Output
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do – while Loopdo – while Loop The do-while loop executes certain statements till the specified
condition is True.
These loops are similar to the while loops, except that a do-while
loop executes at least once, even if the specified condition is False. The
syntax is:
do
{
action statements;
.
.
} while (condition);
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ExampleExampleclass DoWhileDemo{public static void main(String [] args){int count = 1, sum = 0;do{
sum += count;count++;
}while (count <= 100);System.out.println("The sum of first 100 numbers
is : " + sum);}
}
The sum of first 100 numbers is : 5050
Output
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for Loopfor Loop All loops have some common features: a counter variable that is initialized before the
loop begins, a condition that tests the counter variable and a statement that modifies
the value of the counter variable.
The for loop provides a compact format for incorporating these features.
Syntax:
for (initialization statements; condition; increment / decrement statements)
{
action statements;
.
.
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ExampleExampleclass ForDemo{
public static void main(String [] args){
int count = 1, sum = 0;for (count = 1; count <= 10; count += 2){
sum += count;}System.out.println("The sum of first 5 odd
numbers is : " + sum);}
}
The sum of first 5 odd numbers is : 25
Output
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Jump StatementsJump StatementsThree jump statements are:
◦break◦continue◦return
The three uses of break statements are: ◦It terminates a statement sequence in a switch
statement.◦It can be used to exit a loop.◦It is another form of goto.
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ExampleExampleclass BrDemoAppl{
public static void main(String [] args){
for (int count = 1; count <= 100; count++)
{ if (count == 10)
break; System.out.println("The value of
num is : " + count); }
System.out.println("The loop is over");}
}
The value of num is : 1The value of num is : 2The value of num is : 3The value of num is : 4The value of num is : 5The value of num is : 6The value of num is : 7The value of num is : 8The value of num is : 9The loop is over
Output
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SummarySummary A Java program consists of a set of classes. A program may contain comments.
The compiler ignores this commented lines.
The Java program must have a main() method from where it begins its
execution.
Classes define a template for units that store data and code related to an entity.
Variables defined in a class are called the instance variables.
There are two types of casting:widening and narrowing casting.
Variables are basic unit of storage.
Each variable has a scope and lifetime.
Arrays are used to store several items of same data type in consecutive memory
locations.
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Summary Contd…Summary Contd… Java provides different types of operators. They include:
◦ Arithmetic
◦ Bitwise
◦ Relational
◦ Logical
◦ Conditional
◦ Assignment
Java supports the following programming constructs:
◦ if-else
◦ switch
◦ for
◦ while
◦ do-while The three jump statements-break,continue and return helps to transfer
control to another part of the program.
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