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Example of a Java program?

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Cards (28)

Section 1

(28 cards)

Example of a Java program?

Front

class Hello { public static void main ( String[] args ) { System.out.println("Hello World!"); } }

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Comments in Java

Front

Java supports single line and multi-line comments very similar to c and c++. All characters available inside any comment are ignored by Java compiler. public class MyFirstJavaProgram{ /* This is my first java program. * This will print 'Hello World' as the output * This is an example of multi-line comments. */ public static void main(String []args){ // This is an example of single line comment / This is also an example of single line comment. / System.out.println("Hello World"); } }

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Java Access Modifiers:

Front

Java provides a number of access modifiers to set access levels for classes, variables, methods and constructors. The four access levels are: Visible to the package. the default. No modifiers are needed. Visible to the class only (private). Visible to the world (public). Visible to the package and all subclasses (protected).

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Java

Front

Java is a programming language (audio)

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Reference Data Types:

Front

Reference variables are created using defined constructors of the classes. They are used to access objects. These variables are declared to be of a specific type that cannot be changed. For example, Employee, Puppy etc. Class objects, and various type of array variables come under reference data type. Default value of any reference variable is null. A reference variable can be used to refer to any object of the declared type or any compatible type. Example : Animal animal = new Animal("giraffe");

Back

Class Names

Front

Class Names - For all class names the first letter should be in Upper Case.

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The Relational Operators

Front

Operator Description Example == Checks if the value of two operands are equal or not, if yes then condition becomes true. (A == B) is not true. != Checks if the value of two operands are equal or not, if values are not equal then condition becomes true. (A != B) is true. > Checks if the value of left operand is greater than the value of right operand, if yes then condition becomes true. (A > B) is not true. < Checks if the value of left operand is less than the value of right operand, if yes then condition becomes true. (A < B) is true. >= Checks if the value of left operand is greater than or equal to the value of right operand, if yes then condition becomes true. (A >= B) is not true. <= Checks if the value of left operand is less than or equal to the value of right operand, if yes then condition becomes true. (A <= B) is true.

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Primitive Data Types:

Front

There are eight primitive data types supported by Java. Primitive data types are predefined by the language and named by a key word. Let us now look into detail about the eight primitive data types. byte short int long float double boolean char

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Java Basic Syntax

Front

Object - Objects have states and behaviors. Example: A dog has states-color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class. Class - A class can be defined as a template/ blue print that describe the behaviors/states that object of its type support. Methods - A method is basically a behavior. A class can contain many methods. It is in methods where the logics are written, data is manipulated and all the actions are executed. Instant Variables - Each object has its unique set of instant variables. An object's state is created by the values assigned to these instant variables.

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Java Literals:

Front

A literal is a source code representation of a fixed value. They are represented directly in the code without any computation. Literals can be assigned to any primitive type variable. For example: byte a = 68; char a = 'A' String literals in Java are specified like they are in most other languages by enclosing a sequence of characters between a pair of double quotes. Examples of string literals are: "Hello World" "two
lines" "\"This is in quotes\"" Java language supports few special escape sequences for String and char literals as well. They are: Notation Character represented
Newline (0x0a) \r Carriage return (0x0d) \f Formfeed (0x0c) \b Backspace (0x08) \s Space (0x20) \t tab \" Double quote \' Single quote \\ backslash \ddd Octal character (ddd) \uxxxx Hexadecimal UNICODE character (xxxx)

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Case Sensitive

Front

Case Sensitivity - Java is case sensitive which means identifier Hello and hello would have different meaning in Java.

Back

What is Java?

Front

Object Oriented Platform independent: Simple Secure Architectural- neutral Portable Robust Multi-threaded Interpreted High Performance Distributed Dynamic

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Java Variables:

Front

We would see following type of variables in Java: Local Variables Class Variables (Static Variables) Instance Variables (Non static variables)

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Java Arrays:

Front

Arrays are objects that store multiple variables of the same type. However an Array itself is an object on the heap. We will look into how to declare, construct and initialize in the upcoming chapters.

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Java Basic Operators:

Front

Java provides a rich set of operators to manipulate variables. We can divide all the Java operators into the following groups:

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Applet

Front

An applet is a Java bytecode program that runs on a Web browser.

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Program File Name

Front

Program File Name - Name of the program file should exactly match the class name.

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Java Identifiers

Front

All Java components require names. Names used for classes, variables and methods are called identifiers. In java there are several points to remember about identifiers. They are as follows: All identifiers should begin with a letter (A to Z or a to z ), currency character ($) or an underscore (_). After the first character identifiers can have any combination of characters. A key word cannot be used as an identifier. Most importantly identifiers are case sensitive. Examples of legal identifiers:age, $salary, _value, __1_value Examples of illegal identifiers : 123abc, -salary

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What is a Java bytecode?

Front

A Java bytecode is a machine instruction for a Java processor. A file of bytecodes is a machine language program for a Java processor. (audio)

Back

Java Keywords:

Front

The following list shows the reserved words in Java. These reserved words may not be used as constant or variable or any other identifier names. abstract assert boolean break byte case catch char class const continue default do double else enum extends final finally float for goto if implements import instanceof int interface long native new package private protected public return short static strictfp super switch synchronized this throw throws transient try void volatile while

Back

Object

Front

Objects have states and behaviors. Example: A dog has states-color, name, breed as well as behaviors -wagging, barking, eating. An object is an instance of a class.

Back

Class

Front

A class can be defined as a template/ blue print that describe the behaviors/states that object of its type support.

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Data Types in Java

Front

There are two data types available in Java: Primitive Data Types Reference/Object Data Types

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The Arithmetic Operators

Front

The Arithmetic Operators: Operator Description Example + Addition - Adds values on either side of the operator A + B will give 30 - Subtraction - Subtracts right hand operand from left hand operand A - B will give -10 Multiplication - Multiplies values on either side of the operator A B will give 200 / Division - Divides left hand operand by right hand operand B / A will give 2 % Modulus - Divides left hand operand by right hand operand and returns remainder B % A will give 0 ++ Increment - Increase the value of operand by 1 B++ gives 21 -- Decrement - Decrease the value of operand by 1 B-- gives 19

Back

Java Modifiers:

Front

Like other languages, it is possible to modify classes, methods, etc., by using modifiers. There are two categories of modifiers. Access Modifiers : default, public , protected, private Non-access Modifiers : final, abstract, strictfp We will be looking into more details about modifiers in the next section.

Back

Method Name

Front

Method Names - All method names should start with a Lower Case letter. If several words are used to form the name of the method, then each inner word's first letter should be in Upper Case. Example public void myMethodName()

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Bytecodes

Front

(visual)

Back

Java Enums:

Front

Enums were introduced in Java 5.0. Enums restrict a variable to have one of only a few predefined values. The values in this enumerated list are called enums. With the use of enums it is possible to reduce the number of bugs in your code. For example if we consider an application for a fresh juice shop it would be possible to restrict the glass size to small, medium and Large. This would make sure that it would not allow anyone to order any size other than the small, medium or large. class FreshJuice{ enum FreshJuiceSize{ SMALL, MEDIUM, LARGE } FreshJuiceSize size; } public class FreshJuiceTest{ public static void main(String args[]){ FreshJuice juice = new FreshJuice(); juice.size = FreshJuice. FreshJuiceSize.MEDIUM ; System.out.println("Size :" + juice.size); } }

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