Java 基础(四种访问权限修饰符)

Java 权限修饰符 public、protected、(缺省)、private 置于类的成员定义前，用来限定对象对该类成员的访问权限。

对于 class 的权限修饰符只可以用 public 和 default(缺省)

1. public 类可以在任意地方被访问
2. default 类只可以被同一个包内部的类访问

| 修饰符 | 类内部 | 同一个包 | 不同包的子类 | 同一个工程 |
| ---- | ---- | ---- | ---- | ---- | ---- |
| private | yes | | | |
| (缺省) | yes | yes | | |
| protected | yes | yes | yes | |
| public | yes | yes | yes | yes |

例子

Order.java

package com.klvchen.java2;

public class Order {
	
	private int orderPrivate;
	int orderDefault;
	protected int orderProtected;
	public int orderPublic;
	
	private void methodPrivate() {
		orderPrivate = 1;
		orderDefault = 2;
		orderProtected = 3;
		orderPublic = 4;
	}
	
	void methodDefault() {
		orderPrivate = 1;
		orderDefault = 2;
		orderProtected = 3;
		orderPublic = 4;
	}
	
	protected void methodProtected() {
		orderPrivate = 1;
		orderDefault = 2;
		orderProtected = 3;
		orderPublic = 4;
	}
	
	public void methodPublic() {
		orderPrivate = 1;
		orderDefault = 2;
		orderProtected = 3;
		orderPublic = 4;
	}
	

}

OrderTest.java

package com.klvchen.java2;

public class OrderTest {
	public static void main(String[] args) {
		Order order = new Order();
		
		order.orderDefault = 1;
		order.orderProtected = 2;
		order.orderPublic = 3;
		
		order.methodDefault();
		order.methodProtected();
		order.methodPublic();
		
		// 同一个包中的其他类，不可以调用Order类中私有的属性，方法
//		order.orderPrivate = 4;
//		order.methodPrivate();
	}

}

SubOrder.java

package com.klvchen.java3;

import com.klvchen.java2.Order;

public class SubOrder extends Order {
	
	public void method() {
		orderProtected = 1;
		orderPublic = 2;
		
		methodProtected();
		methodPublic();
		
		// 在不同包的子类中，不能调用Order类中声明为 private 和 缺省权限的属性、方法
//		orderPrivate = 3;
//		orderDefault = 4;
//		methodPrivate();
//		methodDefault();
	}

}

OrderTest.java

package com.klvchen.java3;

import com.klvchen.java2.Order;

public class OrderTest {
	public static void main(String[] args) {
		
		Order order = new Order();
		order.orderPublic = 1;
		order.methodPublic();
		
		//不同包下的普通类(非子类)要使用Order类, 不可以调用声明为 private, 缺省, protected权限的属性，方法
//		order.orderPrivate = 2;
//		order.orderDefault = 3;
//		order.orderProtected = 4;

//		order.methodPrivate();
//		order.methodDefault();
//		order.methodProtected();
	}

}