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A
class library is a set
- f
CBOP3203 A class library is a set of classes that supports - - PowerPoint PPT Presentation
CBOP3203 A class library is a set of classes that supports - - PowerPoint PPT Presentation
CBOP3203 A class library is a set of classes that supports the development of programs. Java contains an extensive library of pre- written classes you can use in your programs. These classes are divided into groups called packages
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Package
- Groups class definitions together for privileged access,
lets other classes in the package see more details.
- Generally a way of grouping a set of library routines.
Example packages from Java’s standard class
library:
Package Class Use java.util Scanner Random Inputting from keyboard and files Generates random numbers java.lang Math String Various math constants and functions Handling text java.text DecimalFormat Formatting decimal numbers
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Classes and Java library packages
Classes and Java library packages
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Using Package
- There are two ways we can use public class in a
package:
- 1. Using its absolute name; and
- 2. Using the keyword import.
Using Absolute Name
- java.util.Date DATE = new java.util.Date();
Using import Keyword
- import java.util.*;
- Date DATE = new Date();
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To use a package in a program, it must first be
imported.
Add the import declaration at the beginning of a
program, after the package statement and before any other executable code.
- import packageName.*;
Imports all classes in packageName.
- import packageName.className;
Imports one className from packageName
- Example: import java.text.DecimalFormat;
Imports only the DecimalFormat class from the java.text package.
- The java.lang package does not have to be imported.
String and Math methods are always available.
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//in the Draggable.java file package graphics; public interface Draggable { . . . } //in the Graphic.java file package graphics; public abstract class Graphic { . . . } //in the Circle.java file package graphics; public class Circle extends Graphic implements Draggable { . . . }
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package first; class classB { // most of your code } package first; class classA { classB b = … new classB(); }
Being declared in the same package will allow each class to access each other without extra work. classA using g classB classA.java classB.java
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package second; class classB { // most of your code } package first; import second; class classA { classB b = … new classB(); }
Being declared in the different package will require the use
- f import to
access each other. classA.java classB.java
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ja
java va.l .lan ang
- Provides classes that are fundamental to the design
- f the Java programming language.
- The compiler for each Java program automatically
calls this package. It consists of the basic classes for java language like object, String and System. It also consists
- f
wrapper classes like Integer, Characters and Float that can be used to change the data from the primitive object.
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ja
java va.uti util
- The package consists of general-purpose
classes to be used in a class. The general-purpose classes are general data structure, bit class, time, date, day, string manipulation, random number generator, etc.
ja
java va.io io
- This package provides classes that deals with input
stream and output to be read and printed into a file, stream and
- ther
resources like network socket.
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java.net
- This package can support network application like URL,
TCP socket, UDP socket, IP address and also binary to text conversion.
java.awt
- This package provides interface characteristic like
window, dialog box, button, choices box, list, menu, scroll bar and test space. For more details of java packages visit: http://java.sun.com/javase/7/docs/api/ Or http://doc.java.sun.com/DocWeb/
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