Java protected 作用

作用域       当前类    同一package   子孙类     其他package 

public           √                 √                   √                   √ 

protected     √                 √                   √                   × 

friendly        √                 √                   ×                   × 

private        √                  ×                   ×                   × 

 

不同 modifier 的作用如上图所示： public > protected > package >private

 

但是 protected 具体在什么场合下应用呢？

“ Generally, if something is not deliberately conceived as public, I make it private.

If a situation arises where I need access to that private variable or method from a derived class, I change it from private to protected. ”

一般来说，如果不想被类之外的访问，则设为 private.

但是如果想让某些变量或者 method 可以在子类中访问，就可以把这些变量或者 method 设为 protected. 因此 protected 主要是在继承中的应用。

 

public class Animal {
	protected String name;
	
	public Animal(String name) {
		this.name = name;
	}
	
	public void printName() {
		System.out.println(name);
	}
}

public class Bird extends Animal {

	public Bird(String name) {
		super(name);
	}
	
	public void printBird() {
		System.out.println(name);
	}
	
}