oo.day02
Shoot射击游戏第一天:
1.创建了6个对象类，并创建World类测试
Shoot射击游戏第二天:
1.给6个对象类添加构造方法，并测试
回顾:
1.什么是类？什么是对象?
2.如何创建类？如何创建对象？如何访问成员？
笔记:
0.方法的签名:方法名+参数列表
1.方法的重载(Overload):
1)发生在一个类中，方法名称相同，参数列表不同，方法体不同
2)编译器在编译时根据方法的签名自动绑定调用的方法
2.构造方法:构造函数/构造器/构建器
1)给成员变量赋初值
2)与类同名，没有返回值类型
3)在创建(new)对象时被自动调用
4)若自己不写构造方法，则编译器默认一个无参构造方法
若自己写了构造方法，则编译器不再默认提供
5)构造方法可以重载
3.this:指代当前对象，哪个对象调用方法它指的就是哪个对象
只能用在方法中，方法中访问成员变量之前默认有个this.
this的用法:
1)this.成员变量名---------访问成员变量
2)this.方法名()-----------调用方法(一般不用)
3)this()------------------调用构造方法
4.null:空，没有指向任何对象
若引用的值为null，则该引用不能再进行任何操作了，
若操作则发生NullPointerException空指针异常
5.引用类型变量画等号:
1)指向同一个对象
2)通过一个引用对数据的修改会影响另一个引用对数据的访问
eg:房子钥匙
基本类型变量画等号:
1)赋值
2)对一个变量的修改不会影响另一个变量的访问
eg:身份证复印件
练习:
1)画图
2)将今天的项目代码在昨天基础之上重做两次
房子:对象
房子钥匙:引用
配一把钥匙:引用
内存管理:由JVM来管理的
1)堆:new出来的对象(包括成员变量)
2)栈:局部变量(包括方法的参数)
3)方法区:.class字节码文件(包括方法)
void show(int a){
double b = 34.567;
}
Student zs = new Student();
x = (int)(Math.random()*(400-this.width));
Random rand = new Random();
x = rand.nextInt(400-this.width);
y =
class Student{
String name;
int age;
String address;
Student zs = new Student("zhangsan"); //zhangsan,0,null
Student zs = new Student("zhangsan",25); //zhangsan,25,null
Student zs = new Student("zhangsan",25,"LF"); //zhangsan,25,LF
Student zs = new Student("zhangsan",25); //zhangsan,25,null
Student zs = new Student("zhangsan"); //zhangsan,0,null
Student(String name){
this(name,0);
}
Student(String name,int age){
this(name,age,null);
}
Student(String name,int age,String address){
this.name = name;
this.age = age;
this.address = address;
}
}
Student zs = new Student("zhangsan",25,"LF");
Student ls = new Student("lisi",26,"JMS");
class Student{
String name;
int age;
String address;
Student(String name,int age,String address){
this.name = name; //ls.name="lisi"
this.age = age; //ls.age=26
this.address = address; //ls.address="JMS"
}
}
就近原则
当成员变量与局部变量同名时，this不能省略
class Student{
String name; //成员变量
int age;
String address;
Student(String name,int age,String address){ //局部变量
this.name = name;
this.age = age;
this.address = address;
}
void study(){
System.out.println(name+"在学习...");
}
void sayHi(){
System.out.println("大家好，我叫"+name+"，今年"+age+"岁了，家住"+address);
}
}
Student zs = new Student();
zs.name = "zhangsan";
zs.age = 25;
zs.address = "LF";
zs.study();
zs.sayHi();
Student ls = new Student();
ls.name = "lisi";
ls.age = 26;
ls.address = "JMS";
ls.study();
ls.sayHi();
Student ww = new Student();
ww.study();
ww.sayHi();
class Student{
String name=null;
int age=0;
String address=null;
void study(){ ww.name
System.out.println(this.name+"在学习...");
}
void sayHi(){ ww.name ww.age ww.address
System.out.println("大家好，我叫"+this.name+"，今年"+this.age+"岁了，家住"+this.address);
}
}
class Student{
String name;
int age;
String address;
Student(){
}
//给成员变量赋初值
Student(String name1,int age1,String address1){
name = name1;
age = age1;
address = address1;
}
}
Student zs = new Student();
Student zs = new Student("zhagnsan",25,"LF");
class Student{
String name;
int age;
String address;
//给成员变量赋初值
Student(String name1,int age1,String address1){
name = name1;
age = age1;
address = address1;
}
}
Student zs = new Student(); //编译错误
Student zs = new Student("zhangsan",25,"LF");
Student zs = new Student("zhangsan",25,"LF");
Student ls = new Student("lisi",26,"JMS");
class Student{
String name;
int age;
String address;
//给成员变量赋初值
Student(String name1,int age1,String address1){
name = name1;
age = age1;
address = address1;
}
}
//1)创建一个学生对象
//2)给成员变量赋默认值
//3)调用Student类的构造方法
Student zs = new Student();
Student zs = new Student();
zs.setInfo("zhangsan",25,"河北廊坊");
Student ls = new Student();
ls.setInfo("lisi",26,"黑龙江佳木斯");
Student zs = new Student();
zs.name = "zhangsan";
zs.age = 25;
zs.address = "河北廊坊";
Student ls = new Student();
ls.name = "lisi";
ls.age = 26;
ls.address = "黑龙江佳木斯";
void println(){
}
void println(int a){
}
void println(double a){
}
void println(boolean a){
}
void println(char a){
}
void println(String a){
}
System.out.println();
System.out.println(23);
System.out.println(35.7);
System.out.println(true);
System.out.println('你');
System.out.println("Hello");