Thinking in java 笔记----权限访问控制

 一、Java访问权限控制

1）在类的内部都可以访问到四种权限

package com.learn.permission;

public class TestPermission {
	private String privateStr = "private";
	protected String protectedStr = "protected";
	public String pulicStr = "public";
	String packageStr = "package";
	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TestPermission test = new TestPermission();
		System.out.println(test.pulicStr);
		System.out.println(test.packageStr);
		System.out.println(test.protectedStr);
		System.out.println(test.privateStr);
	}	
}

2）同一包内不同类，private不可见

package com.learn.permission;

public class TestInPackage {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TestPermission test = new TestPermission();
		System.out.println(test.pulicStr);
		System.out.println(test.packageStr);
		System.out.println(test.protectedStr);
//		System.out.println(test.privateStr); //private is not visible in different class of same pacakge

	}
}

3）同一包里子类，private不可见

package com.learn.permission;

public class TestPermissionExtends extends TestPermission {
	public static void main(String[] args){
		TestPermissionExtends test = new TestPermissionExtends();
		System.out.println(test.pulicStr);
		System.out.println(test.packageStr);
		System.out.println(test.protectedStr);
		//after extend , the private field or method is not available
//		System.out.println(test.privateStr);
	}
}

4) 不同包非子类，只有public可见

package com.learn.chapter1;

import com.learn.permission.TestPermission;


public class TestOutPackage {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		// TODO Auto-generated method stub
		TestPermission test = new TestPermission();
		System.out.println(test.pulicStr);
		//outside the package , only the public is available
//		System.out.println(test.packageStr);
//		System.out.println(test.protectedStr);
//		System.out.println(test.privateStr);
	}

}

5）不同包里子类，只有public和protected可见

package com.learn.chapter1;

import com.learn.permission.TestPermission;

public class TestPermissionExtend extends TestPermission {
	public static void main(String[] args){
		TestPermissionExtend test = new TestPermissionExtend();
		System.out.println(test.pulicStr);
//		System.out.println(test.packageStr);
		System.out.println(test.protectedStr);
		//after extend , the private field or method is not available
//		System.out.println(test.privateStr);
	}
}

 总结：

Public：对任意类可见

protected ：与包访问权限类似，只是被继承的时候可见，这个时候相当于private，不过仍可以继承可见

包访问权限：只对当前包可见

private ：只对当前类可见