instanceof

• 判断对象类型是不是父子关系

public class Person
{
}

public class Student extends Person
{
}

public class Teacher extends Person
{
}

public class Application
{
	public static void main(String[] args){
		//Object>Person>Student
		//Object>Person>Teacher
		//Object>String
		Object object = new Student();
		System.out.println(object instanceof Student);//ture
		System.out.println(object instanceof Person);//ture
		System.out.println(object instanceof Object);//ture
		System.out.println(object instanceof Teacher);//false
		System.out.println(object instanceof String);//false
		
	}
}

• 注意：同级之间不能比较

public class Application
{
	public static void main(String[] args){
		//Object>Person>Student
		//Object>Person>Teacher
		//Object>String
	 Student object = new Student();//数据类型变为Student，与Teacher无法比较
		System.out.println(object instanceof Student);//ture
		System.out.println(object instanceof Person);//ture
		System.out.println(object instanceof Object);//ture
		System.out.println(object instanceof Teacher);//false
		System.out.println(object instanceof String);//false
		
	}
}

类型转换

• 低转高，自动转换；高转低，强制转换

public class Student extends Person
{
	public void go(){
		System.out.println("go");
	}
}

public class Application
{
	public static void main(String[] args){
		Person human = new Student();
		((Student)human).go();//human.go ()由Person转为Student，高转低需要强制转换。
		
	}
}