每日一练
递归求汉诺塔
package day0801;
import java.util.Scanner;
public class Test1 {
public static void main(String[] args) {
System.out.print("玩几层汉诺塔:");
int i = new Scanner(System.in).nextInt();
f(i);
}
private static void f(int i) {
f(i,"A","B","C");
}
private static void f(int i, String a, String b, String c) {
if(i==1) {
System.out.println(a+"->"+c);
return;
}
//n-1 A->C->B
f(i-1,a,c,b);
System.out.println(a+"->"+c);
//n-1 b->a->c
f(i-1,b,a,c);
}
}
继承
目的:代码重用
单继承
不继承:构造方法/私有成员
子类对象:调用成员时,先子类后父类
方法重写:继承的方法在子类中重新编写
父类构造方法:super()必须是首行代码
super.xxx():调用父类成员
电子宠物
package day0802;
import java.util.Random;
import java.util.Scanner;
public class Test1 {
public static void main(String[] args) {
System.out.println("1.猫");
System.out.println("2.狗");
System.out.print("选择:");
int i = new Scanner(System.in).nextInt();
System.out.print("给宠物起个名字");
String s = new Scanner(System.in).nextLine();
Dog dog = null;
Cat cat = null;
if(i == 1){
cat = new Cat(s);
play(cat);
}else if(i == 2){
dog = new Dog(s);
play(dog);
}
}
private static void play(Cat cat) {
System.out.println("按回车继续");
while (true)
{
int i = new Random().nextInt(3);
switch (i)
{
case 0: cat.feed();break;
case 1: cat.punish();break;
case 2: cat.play();break;
}
new Scanner(System.in).nextLine();
}
}
private static void play(Dog dog) {
System.out.println("按回车继续");
while (true)
{
int i = new Random().nextInt(3);
switch (i)
{
case 0: dog.feed();break;
case 1: dog.punish();break;
case 2: dog.play();break;
}
new Scanner(System.in).nextLine();
}
}
}
package day0802;
public class Pet {
String name;
int full;
int happy;
public Pet(String name)
{
this(name,50,50);
}
public Pet(String name,int full,int happy)
{
this.full = full;
this.happy = happy;
this.name = name;
}
public void feed()
{
if(full > 90)
{
System.out.println(name+"已经吃饱了");
return;
}
System.out.println("给"+name+"喂食");
full+=10;
System.out.println("饱食度:"+full);
}
public void play()
{
if(full <= 0)
{
System.out.println(name+"玩不动了");
return;
}
System.out.println("陪"+name+"玩耍");
full-=10;
happy+=10;
System.out.println("饱食度:"+full+"快乐度:"+happy);
}
public void punish()
{
//TODO:要能让不同宠物有不同的行为
System.out.println("惩罚"+name+cry());
happy-=10;
System.out.println("快乐度:"+happy);
}
public String cry() {
return "";
}
}
package day0802;
public class Cat extends Pet {
public Cat(String name) {
super(name);
}
public Cat(String name, int full, int happy) {
super(name, full, happy);
}
@Override
public String cry()
{
return "喵喵喵";
}
}
package day0802;
public class Dog extends Pet {
public Dog(String name) {
super(name);
}
public Dog(String name, int full, int happy) {
super(name, full, happy);
}
@Override
public String cry()
{
return "汪汪汪";
}
}
object是所有类的顶层父类
object的toString()方法返回:类名@内存地址值
多态
所用:一致的类型
子类型对象,可以被当作父类型来处理
节省代码
类型转换:
向上转型:子类的对象转型为父类型
向下转型:已经转成父类型的子类对象,再转回成子类型
instanceof
运行期类型识别
对真实类型和父类型判断，都得到 true
Shape s = new Line();
instanceof Line true
instanceof Shape true
instanceof Object true
package day0705;
public class Test1 {
public static void main(String[] args) {
Person person = new Person("张三", 22,"男");
Student student = new Student();
Employee employee = new Employee();
student.name = "李四";
student.gender = "女";
student.age = 18;
student.school = "家里蹲大学";
employee.name = "王五";
employee.gender = "女";
employee.age = 17;
employee.salary = 12000;
/*System.out.println(person.toString());
System.out.println(student.toString());
System.out.println(employee.toString());*/
f(person);
f(student);
f(employee);
}
static void f(Person p)
{
System.out.println(p.toString());
}
}
package day0705;
public class Test3 {
public static void main(String[] args) {
Student s = new Student();
Person p = s;
}
}