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The document discusses several key aspects of the Java programming language: 1. Java is platform independent and object-oriented, with programs constructed of classes that group data and methods. 2. Source code is compiled to bytecode, then executed by the Java Virtual Machine on any system. 3. Classes describe objects via their common characteristics as blueprints, including data fields and methods. 4. The Java API provides commonly used packages like Swing for GUIs.

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30 views

Co1 2

The document discusses several key aspects of the Java programming language: 1. Java is platform independent and object-oriented, with programs constructed of classes that group data and methods. 2. Source code is compiled to bytecode, then executed by the Java Virtual Machine on any system. 3. Classes describe objects via their common characteristics as blueprints, including data fields and methods. 4. The Java API provides commonly used packages like Swing for GUIs.

Uploaded by

deepika5334
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
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Download as PPTX, PDF, TXT or read online on Scribd
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Salient Characteristics of Java

• Java is platform independent: the same program can run on any correctly
implemented Java system
• Java is object-oriented:
– Structured in terms of classes, which group data with operations on
that data
– Can construct new classes by extending existing ones
• Java designed as
– A core language plus
– A rich collection of commonly available packages
• Java can be embedded in Web pages
Java Processing and Execution

• Begin with Java source code in text files: Model.java


• A Java source code compiler produces Java byte code
– Outputs one file per class: Model.class
– May be standalone or part of an IDE
• A Java Virtual Machine loads and executes class files
– May compile them to native code (e.g., x86) internally
Compiling and Executing a Java Program
Classes and Objects

• The class is the unit of programming


• A Java program is a collection of classes
– Each class definition (usually) in its own .java file
– The file name must match the class name
• A class describes objects (instances)
– Describes their common characteristics: is a blueprint
– Thus all the instances have these same characteristics
• These characteristics are:
– Data fields for each object
– Methods (operations) that do work on the objects
The Java API

• API = Application Programming Interface


• Java = small core + extensive collection of packages
• A package consists of some related Java classes:
– Swing: a GUI (graphical user interface) package
– AWT: Application Window Toolkit (more GUI)
– util: utility data structures (important to CS 187!)
• The import statement tells the compiler to make available classes and
methods of another package
• A main method indicates where to begin executing a class (if it is designed
to be run as a program)
A Little Example of import and main

import javax.swing.*;
// all classes from javax.swing
public class HelloWorld { // starts a class
public static void main (String[] args) {
// starts a main method
// in: array of String; out: none (void)
}
}
• public = can be seen from any package
• static = not “part of” an object
Processing and Running HelloWorld

• javac HelloWorld.java
– Produces HelloWorld.class (byte code)
• java HelloWorld
– Starts the JVM and runs the main method
Primitive Data Types

• Represent numbers, characters, boolean values


• Integers: byte, short, int, and long
• Real numbers: float and double
• Characters: char
Primitive Data Types
Operators

1. subscript [ ], call ( ), member access .


2. pre/post-increment ++ --, boolean complement !, bitwise complement ~, unary + -,
type cast (type), object creation new
3. */%
4. binary + - (+ also concatenates strings)
5. signed shift << >>, unsigned shift >>>
6. comparison < <= > >=, class test instanceof
7. equality comparison == !=
8. bitwise and &
9. bitwise or |
11. logical (sequential) and &&
12. logical (sequential) or ||
13. conditional cond ? true-expr : false-expr
14. assignment =, compound assignment += -= *= /= <<= >>= >>>= &= |
=
Java Control Statements

• A group of statements executed in order is written


– { stmt1; stmt2; ...; stmtN; }
• The statements execute in the order 1, 2, ..., N
• Control statements alter this sequential flow of execution
Java Control Statements (continued)
Java Control Statements (continued)

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