Java (package)

Java

  • 1

  • 2

  • 3

Java packageclassenumerationsannotation

package pkg1[pkg2[pkg3]];

,Something.java

package net.java.util; public class Something{ ... }

net/java/util/Something.java package() java java

package

Java

  • java.lang-
  • java.io-

namespace

unnamed package

animals

animals interface

Animal.java

/* : Animal.java */ package animals; interface Animal { public void eat(); public void travel(); }

MammalInt.java

package animals; /* : MammalInt.java */ public class MammalInt implements Animal{ public void eat(){ System.out.println("Mammal eats"); } public void travel(){ System.out.println("Mammal travels"); } public int noOfLegs(){ return 0; } public static void main(String args[]){ MammalInt m = new MammalInt(); m.eat(); m.travel(); } }

animals 

$ mkdir animals
$ cp Animal.class  MammalInt.class animals
$ java animals/MammalInt
Mammal eats
Mammal travel

import

Java

Java import

import

java import Java

import package1[.package2].(classname|*);

import package

// package package com.example; // import import java.util.ArrayList; import java.util.List; // public class MyClass { // }

import

import com.runoob.MyClass;

MyClass

* 

import com.runoob.mypackage.*;

com.runoob.mypackage *

.

import java.util.ArrayList; // java.util ArrayList
import java.util.*; // java.util

import com.example.MyClass; // com.example MyClass
import com.example.*; // com.example

payroll Employee payroll Boss Boss Employee payroll Boss

Boss.java

package payroll; public class Boss { public void payEmployee(Employee e) { e.mailCheck(); } }

Boss payroll Boss

payroll.Employee

import *

import payroll.*;

import Employee

import payroll.Employee;

import import

package

java

.java

// : Car.java package vehicle; public class Car { // }

....\vehicle\Car.java

  • -> vehicle.Car

  • -> vehicle\Car.java ( windows )

. runoob.com com.runoob

com.runoob.test Runoob.java

....\com\runoob\test\Runoob.java

.class

// : Runoob.java package com.runoob.test; public class Runoob { } class Google { }

-d 

$javac -d . Runoob.java


.\com\runoob\test\Runoob.class
.\com\runoob\test\Google.class

\com\runoob\test\ 

import com.runoob.test.*;

.class .java .class .java 

<path-one>\sources\com\runoob\test\Runoob.java
<path-two>\classes\com\runoob\test\Google.class

java JVM

class path CLASSPATH java package class path .class

<path- two>\classes class pathpackage com.runoob.test, JVM <path-two>\classes\com\runoob\test .class

class path JVM JAR Java class path

CLASSPATH

CLASSPATH

  • Windows DOS C:\> set CLASSPATH
  • UNIX Bourne shell # echo $CLASSPATH
CLASSPATH
  • Windows DOS C:\> set CLASSPATH=
  • UNIX Bourne shell # unset CLASSPATH; export CLASSPATH

CLASSPATH:

  • Windows DOS C:\> set CLASSPATH=C:\users\jack\java\classes
  • UNIX Bourne shell # CLASSPATH=/home/jack/java/classes; export CLASSPATH