万物皆对象
学习程序的目的：解决现实的问题。
前提：模拟现实世界
小明（人） – 人类
public class Human {
String name;
String gender;
int height;
int weight;
}
public class Bear {
}
public class Computer {
}
Human man = new Human(); man.name = "小明"; man.gender = "男"; man.height = 168; man.weight = 160;
实例变量和局部变量的区别：
方法的重载：
方法的签名（唯一性）在一个类中，方法名相同，参数列表不同就叫做方法的重载 今日内容 1. 构造方法
无参构造方法
没有参数 有参构造方法
有参数
定义：
public 类名() {
}
public 类名(参数列表) {
}
构造方法构造方法，不能被直接调用，只能在创建对象时调用（new）如果不自己定义一个构造器，那么系统就默认有一个无参构造方法
一旦自己定义一个构造器（无参，有参都可），那么就没有默认的无参构造方法了
package com.qf;
public class Demo01 {
public static void main(String[] args) {
Person p = new Person();
System.out.println(p);
//表示自己
Student stu = new Student();
stu.name = "小帅哥";
stu.code = "888888";
stu.gender = "男";
stu.cardId = "666999";
Student stu2 = new Student("jackma","9999","男","123456");
String name = stu2.name;
String code = stu2.code;
String gender = stu2.gender;
String cardId = stu2.cardId;
System.out.println("name:"+name+" code:"+code+" gender:"+gender+" cardId:"+cardId);
System.out.println("----------------------------");
Computer c = new Computer("华为",5600,"i5","8G");
}
}
class Person {
public Person() {
System.out.println("执行Person无参构造方法");
}
}
class Student {
String name;
String code;
String gender;
String cardId;
public Student() {
}
public Student(String n, String c, String g, String id) {
System.out.println("执行有参构造方法--");
name = n;
code = c;
gender = g;
cardId = id;
}
}
class Computer {
//定义四个属性 品牌 价格 cpu 内存
String brand;
double price;
String cpu;
String ram;
public Computer(String b, double p, String c, String r) {
brand = b;
price = p;
cpu = c;
ram = r;
}
}
2. this
在有参构造器中,实例变量和局部变量可能会相同
在相同的作用范围中，会优先使用局部变量
可以使用this关键字使用类中的全局变量
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package com.qf;
public class Demo02 {
public static void main(String[] args) {
}
}
class Phone {
String brand;
double price;
String cpu;
String ram;
public Phone(String brand, double price, String cpu, String ram) {
this.brand = brand;
this.price = price;
this.cpu = cpu;
this.ram = ram;
}
public Phone(String brand, double price) {
this.brand = brand;
this.price = price;
}
public Phone(String brand, double price, String cpu) {
this.brand = brand;
this.price = price;
this.cpu = cpu;
}
public Phone(String brand) {
this.brand = brand;
}
public Phone() {
}
}
class Cup {
String brand;
double price;
String name;
int capacity;
public Cup(String brand) {
super();
this.brand = brand;
}
public Cup(double price) {
super();
this.price = price;
}
public Cup(int capacity) {
super();
this.capacity = capacity;
}
public Cup(String brand, double price) {
super();
this.brand = brand;
this.price = price;
}
public Cup(String brand, String name) {
super();
this.brand = brand;
this.name = name;
}
public Cup(String brand, int capacity) {
super();
this.brand = brand;
this.capacity = capacity;
}
}
3. 面向对象特征
抽象，封装，继承，多态
抽象 抽取一个事情重要的特性封装 重要的东西，只能自己用，别人不能获取 属性的私有化继承 类别与类别之间的关系多态 相同的种类，执行相同的操作，得到的结果却不一样 3.1 封装
属性私有为私有属性，添加set，get方法
package com.qf;
public class Person {
private String name;
private String gender;
private int age;
public Person() {
}
//1.1 定义有参构造器，为属性赋值
public Person(int age) {
this.age = age;
}
//1.2 通过实例方法赋值
public void setAge(int age) {
this.age = age;
}
public void setName(String name) {
this.name = name;
}
public void setGender(String gender) {
this.gender = gender;
}
//1.3 获取age值的方法
public int getAge() {
return age;
}
public String getName() {
return name;
}
public String getGender() {
return gender;
}
public void printSelf() {
System.out.println("name:"+name+" gender:"+gender+" age:"+age);
}
}
package com.qf;
public class Phone {
private String brand;
private double price;
private String cpu;
private String ram;
public String getBrand() {
return brand;
}
public void setBrand(String brand) {
this.brand = brand;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public String getCpu() {
return cpu;
}
public void setCpu(String cpu) {
this.cpu = cpu;
}
public String getRam() {
return ram;
}
public void setRam(String ram) {
this.ram = ram;
}
//重写toString
}
package com.qf;
public class Test01 {
public static void main(String[] args) {
Person p = new Person(18);
p.printSelf();
Person p2 = new Person();
p2.setAge(17);
p2.setName("pony");
p2.printSelf();
int age = p2.getAge();
System.out.println();
String name = p2.getName();
System.out.println(name);
Phone phone = new Phone();
phone.setBrand("华为");
phone.setPrice(3500);
phone.setCpu("麒麟");
phone.setRam("8G");
System.out.println(phone);
}
}
