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What are differences between user defined packages and predefined packages in java?
As we know, default package of java.lang.*; is implicitly called if it is not explicitly called Ok, So. Package is Collection Classes ( abstract or interfaces).
Package Creation :-
1 ) First line of the program, in which you want create a package must be a your desired package name starting with package keyword and followed by semicolon.
2 ) While creating package, it is not necessary to write public before each class name.
3 ) But, each and ever method must be public.
Creating or Compiling Package :-
Syntax :-
D:\Practice\Javac -d < Path of program >
Complete Example :-
package TYBCS;
class Mathematics
{
public int addNumbers(int num1,int num2)
{
return(num1+num2);
}
public static double addFloatNum(double num1,double num2,double num3)
{
return(num1+num2+num3);
}
}
class Maximum
{
public int getMaxOutofThree(int n1,int n2,int n3)
{
int num=0;
if(n1>n2 && n1>n3) { num=n1; }
if(n2>n1 && n2>n3) { num=n2; }
if(n3>n1 && n3>n2) { num=n3; }
return num;
}
}
class Practice
{
public static void main(String args[])
{
Mathematics m=new Mathematics();
Maximum mx=new Maximum();
System.out.println("Addition 5+5 : "+m.addNumbers(5,5));
System.out.println("Addition f 2.5+2.5 : "+m.addFloatNum(2.5,2.5,2.5));
System.out.println("Max Number 7, 8 , 1 : "+mx.getMaxOutofThree(7,8,1));
}
}
/*
Output:-
D:\Data>javac -d D:\Data\ Practice.java
D:\Data>java TYBCS.Practice
Addition 5+5 : 10
Addition 2.5+2.5 : 7.5
Max Number 7, 8 , 1 : 8
D:\Data>
*/
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JudyPredefinedpackages and classes are those that come installed as part of the standard Java library; it is expected that each conforming Java implementation will have these libraries available to them without having to package those classes as part of the project. User defined packages, in contrast, are those classes not defined by the Java interface and must be packaged as part of an application (e.g. placed in the JAR file) in order to provide the implementation class files needed to have the program run.
Predefined packages
Java provides various predefined classes and interfaces (API’s) organized under packages. These are known as predefined packages, following is the list of predefined packages in java −
java.lang − This package provides the language basics.
java.util − This packages provides classes and interfaces (API’s) related to collection frame work, events, data structure and other utility classes such as date.
java.io − This packages provides classes and interfaces for file operations, and other input and output operations.
USER Defined pakages
To create a package, we choose a package name and to include the classes, interfaces, enumerations, etc, inside the package, we write the package with its name at the top of every source file.
There can be only one package statement in each type of file. If we do not write class, interfaces, inside any package, then they will be placed in the current default package.
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