标签:instanceof 类型转换 System static Student println public out
instanceof和类型转换
package com.oop;
import com.oop.demo06.Person;
import com.oop.demo06.Student;
import com.oop.demo06.Teacher;
public class Application {
public static void main(String[] args) {
//Object >
Object object = new Student();
System.out.println(object instanceof Student);//true
System.out.println(object instanceof Person);//true
System.out.println(object instanceof Object);//true
System.out.println(object instanceof Teacher);//false
System.out.println(object instanceof String);//false
System.out.println("==================================");
Person person = new Student();
System.out.println(person instanceof Student);//true
System.out.println(person instanceof Person);//true
System.out.println(person instanceof Object);//true
System.out.println(person instanceof Teacher);//false
//System.out.println(person instanceof String);//编译报错!
System.out.println("==================================");
Student student = new Student();
System.out.println(student instanceof Student);//true
System.out.println(student instanceof Person);//true
System.out.println(student instanceof Object);//true
//System.out.println(student instanceof Teacher);//编译报错!
//System.out.println(student instanceof String);//编译报错!
}
}
- 父类引用指向子类对象
- 把子类转换为父类,向上转型
- 把父类转换为子类,向下转型:强制转换
- 方便方法的调用,减少重复使用代码!
package com.oop.demo06;
public class Student extends Person{
public void go(){
System.out.println("go");
}
}
package com.oop;
import com.oop.demo06.Person;
import com.oop.demo06.Student;
public class Application {
public static void main(String[] args) {
//类型之间的转化:父 子
/*
//高 低
Person obj = new Student();
//student将这个对象转换为Student类型,我们就可以使用Student类型的方法了!
((Student)obj).go();
*/
Student student = new Student();
student.go();
Person person = student;
}
}
static关键字详解
package com.oop.demo07;
public class Person {
//2:赋初值~
{
System.out.println("匿名代码块");
}
//1:只执行一次~
static {
System.out.println("静态代码块");
}
//3
public Person() {
System.out.println("构造方法");
}
public static void main(String[] args) {
Person person1 = new Person();
System.out.println("====================");
Person person2 = new Person();
}
}
运行结果
静态代码块
匿名代码块
构造方法
====================
匿名代码块
构造方法
package com.oop.demo07;
//static
public class Student {
private static int age;//静态的变量 多线程!
private double score;//非静态的变量
public void run(){
}
public static void go(){
}
public static void main(String[] args) {
Student s1 = new Student();
System.out.println(Student.age);
System.out.println(s1.age);
System.out.println(s1.score);
}
}
package com.oop.demo07;
//静态导入包~
import static java.lang.Math.random;
import static java.lang.Math.PI;
public class Test {
public static void main(String[] args) {
System.out.println(random());
System.out.println(PI);
}
}
final之后断子绝孙
标签:instanceof,类型转换,System,static,Student,println,public,out 来源: https://www.cnblogs.com/L1sy/p/15613136.html
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