Java封装

包封在Java是包装代码和数据一起成一个单一的单元，例如，它是混合的几种药物的胶囊的方法。

我们可以通过使私有类的所有数据成员在Java中创建一个完全封装类。现在我们可以使用setter和getter方法来设置，并在其中获得数据。

在Java Bean类是完全封装的类的实例。

在Java中封装的优势

通过只提供一个setter或getter方法，可以使课堂只读或只写。换句话说，你可以跳过getter或setter方法。

它为你提供了数据的控制。假设你想设置id的值应该是大于100只，你可以写setter方法内部的逻辑。你可以写逻辑不是负数存储在setter方法。

它是一种实现Java数据隐藏，因为其他类将不能够通过私有数据成员访问数据。

包囊类很容易测试。因此，它是单元测试更好。

该标准的IDE都提供工具来生成getter和setter。因此，很容易和快速地使用Java创建封装类。

在Java中封装的简单示例

让我们来看看封装的简单的例子，只有一个与它的setter和getter方法场。

文件：Student.java

//A Java class which is a fully encapsulated class.
//It has a private data member and getter and setter methods.
package com.srcmini;
public class Student{
//private data member
private String name;
//getter method for name
public String getName(){
return name;
}
//setter method for name
public void setName(String name){
this.name=name
}
}

文件：Test.java

//A Java class to test the encapsulated class.
package com.srcmini;
class Test{
public static void main(String[] args){
//creating instance of the encapsulated class
Student s=new Student();
//setting value in the name member
s.setName("vijay");
//getting value of the name member
System.out.println(s.getName());
}
}

Compile By: javac -d . Test.java
Run By: java com.srcmini.Test

输出：

vijay

只读类

//A Java class which has only getter methods.
public class Student{
//private data member
private String college="AKG";
//getter method for college
public String getCollege(){
return college;
}
}

现在，你不能改变的高校数据成员，这是“AKG”的价值。

s.setCollege("KITE");//will render compile time error

只写类

//A Java class which has only setter methods.
public class Student{
//private data member
private String college;
//getter method for college
public void setCollege(String college){
this.college=college;
}
}

现在，你不能让大学的价值，你只能改变大学的数据成员的值。

System.out.println(s.getCollege());//Compile Time Error，because there is no such method
System.out.println(s.college);//Compile Time Error，because the college data member is private. 
//So，it can't be accessed from outside the class

在Java中封装的另一实施例

让我们看到，只有四个拥有setter和getter方法封装领域的另一个例子。

文件：Account.java

//A Account class which is a fully encapsulated class.
//It has a private data member and getter and setter methods.
class Account {
//private data members
private long acc_no;
private String name，email;
private float amount;
//public getter and setter methods
public long getAcc_no() {
	return acc_no;
}
public void setAcc_no(long acc_no) {
	this.acc_no = acc_no;
}
public String getName() {
	return name;
}
public void setName(String name) {
	this.name = name;
}
public String getEmail() {
	return email;
}
public void setEmail(String email) {
	this.email = email;
}
public float getAmount() {
	return amount;
}
public void setAmount(float amount) {
	this.amount = amount;
}

}

文件：TestAccount.java

//A Java class to test the encapsulated class Account.
public class TestEncapsulation {
public static void main(String[] args) {
    //creating instance of Account class
	Account acc=new Account();
	//setting values through setter methods
	acc.setAcc_no(7560504000L);
	acc.setName("Sonoo Jaiswal");
	acc.setEmail("sonoojaiswal@srcmini02.com");
	acc.setAmount(500000f);
	//getting values through getter methods
	System.out.println(acc.getAcc_no()+" "+acc.getName()+" "+acc.getEmail()+" "+acc.getAmount());
}
}

输出：

7560504000 Sonoo Jaiswal sonoojaiswal@srcmini02.com 500000.0