1.构造方法：

构造函数、构造器、构建器-----------复用给成员变量初始化代码

作用：给成员变量赋初始值
与类同名，没有返回值类型(连void都没有)
在创建(new)对象时被自动调用
若自己不写构造方法，则编译器默认提供一个无参构造方法，
若自己写了构造方法，则不再默认提供
构造方法可以重载

2.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.

2.1this的用法

this.成员变量名--------------访问成员变量
- 当成员变量和局部变量同名时，若想访问成员变量则this不能省略，其它一般省略
this.方法名()------------------调用方法(一般不用，了解)
this()----------------------------调用构造方法(一般不用，了解)

   class Student {//成员变量String name;int age;String address;//构造方法Student(String name,int age,String address){this.name = name;       //zs.name="zhangsan"this.age = age;         //zs.age=25this.address = address; //zs.address="LF"}//方法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);}}//构造方法和this的演示public class ConsDemo {public static void main(String[] args) {//Student zs = new Student(); //编译错误，Student类没有无参构造Student zs = new Student("zhangsan",25,"LF");Student ls = new Student("lisi",26,"JMS");zs.sayHi();ls.sayHi();}}

3.NULL

表示空，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点操作了，若操作则发生NullPointerException空指针异常。

4.潜艇游戏第二天

图解（潜艇y坐标）：

图解（坐标图）：

4.1给6个类添加构造方法，并测试

4.1.1Battleship类

package cn.tedu.submarine;import java.util.Objects;/*** 战舰*/
public class Battleship {/*** 宽*/private int width;/*** 高*/private int height;/*** x轴*/private int x;/*** y轴*/private int y;/*** 命*/private int life;/*** 移动的速度*/private int speed;public Battleship() {this.width = 66;this.height = 26;this.x = 270;this.y = 124;this.life = 5;this.speed = 20;}public Battleship(int width, int height, int x, int y, int life, int speed) {this.width = width;this.height = height;this.x = x;this.y = y;this.life = life;this.speed = speed;}/*** 移动战舰的方法*/public void move(){System.out.println("战舰移动");}/*** 发射炸弹的方法*/public void shootBomb(){}@Overridepublic String toString() {return "Battleship{" +"width=" + width +", height=" + height +", x=" + x +", y=" + y +", life=" + life +", speed=" + speed +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Battleship that = (Battleship) o;return width == that.width &&height == that.height &&x == that.x &&y == that.y &&life == that.life &&speed == that.speed;}@Overridepublic int hashCode() {return Objects.hash(width, height, x, y, life, speed);}public int getWidth() {return width;}public void setWidth(int width) {this.width = width;}public int getHeight() {return height;}public void setHeight(int height) {this.height = height;}public int getX() {return x;}public void setX(int x) {this.x = x;}public int getY() {return y;}public void setY(int y) {this.y = y;}public int getLife() {return life;}public void setLife(int life) {this.life = life;}public int getSpeed() {return speed;}public void setSpeed(int speed) {this.speed = speed;}
}

4.1.2Bomb类

package cn.tedu.submarine;import java.util.Objects;/*** 炸弹*/
public class Bomb {/*** 宽*/private int width;/*** 高*/private int height;/*** x轴*/private int x;/*** y轴*/private int y;/*** 速度*/private int speed;public Bomb(int x , int y) {this.width = 9;this.height = 12;this.x = x;this.y = y;this.speed = 3;}public Bomb(int width, int height, int x, int y, int speed) {this.width = width;this.height = height;this.x = x;this.y = y;this.speed = speed;}/*** 炸弹移动的方法*/public void move(){System.out.println("炸弹移动");}@Overridepublic String toString() {return "Bomb{" +"width=" + width +", height=" + height +", x=" + x +", y=" + y +", speed=" + speed +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Bomb bomb = (Bomb) o;return width == bomb.width &&height == bomb.height &&x == bomb.x &&y == bomb.y &&speed == bomb.speed;}@Overridepublic int hashCode() {return Objects.hash(width, height, x, y, speed);}public int getWidth() {return width;}public void setWidth(int width) {this.width = width;}public int getHeight() {return height;}public void setHeight(int height) {this.height = height;}public int getX() {return x;}public void setX(int x) {this.x = x;}public int getY() {return y;}public void setY(int y) {this.y = y;}public int getSpeed() {return speed;}public void setSpeed(int speed) {this.speed = speed;}
}

4.1.3Mine类

package cn.tedu.submarine;import java.util.Objects;/*** 水雷*/
public class Mine {/*** 宽*/private int width;/*** 高*/private int height;/*** x轴*/private int x;/*** y轴*/private int y;/*** 速度*/private int speed;public Mine(int x , int y) {this.width = 11;this.height = 11;this.x = x;this.y = y;this.speed = 1;}public Mine(int width, int height, int x, int y, int speed) {this.width = width;this.height = height;this.x = x;this.y = y;this.speed = speed;}/*** 水雷移动的方法*/public void move(){System.out.println("水雷移动");}@Overridepublic String toString() {return "Mine{" +"width=" + width +", height=" + height +", x=" + x +", y=" + y +", speed=" + speed +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;Mine mine = (Mine) o;return width == mine.width &&height == mine.height &&x == mine.x &&y == mine.y &&speed == mine.speed;}@Overridepublic int hashCode() {return Objects.hash(width, height, x, y, speed);}public int getWidth() {return width;}public void setWidth(int width) {this.width = width;}public int getHeight() {return height;}public void setHeight(int height) {this.height = height;}public int getX() {return x;}public void setX(int x) {this.x = x;}public int getY() {return y;}public void setY(int y) {this.y = y;}public int getSpeed() {return speed;}public void setSpeed(int speed) {this.speed = speed;}
}

4.1.4MineSubMarine类

package cn.tedu.submarine;import java.util.Objects;
import java.util.Random;/*** 水雷潜艇*/
public class MineSubmarine {/*** 宽*/private int width;/*** 高*/private int height;/*** x轴*/private int x;/*** y轴*/private int y;/*** 速度*/private int speed;public MineSubmarine() {this.width = 63;this.height = 19;Random rand = new Random();x = -width;y = rand.nextInt(479-height-150+1 ) +150;this.speed = rand.nextInt(3)+1;}public MineSubmarine(int width, int height, int x, int y, int speed) {this.width = width;this.height = height;this.x = x;this.y = y;this.speed = speed;}/*** 水雷潜艇移动的方法*/public void move(){System.out.println("水雷潜艇移动");}@Overridepublic String toString() {return "MineSubmarine{" +"width=" + width +", height=" + height +", x=" + x +", y=" + y +", speed=" + speed +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;MineSubmarine that = (MineSubmarine) o;return width == that.width &&height == that.height &&x == that.x &&y == that.y &&speed == that.speed;}@Overridepublic int hashCode() {return Objects.hash(width, height, x, y, speed);}public int getWidth() {return width;}public void setWidth(int width) {this.width = width;}public int getHeight() {return height;}public void setHeight(int height) {this.height = height;}public int getX() {return x;}public void setX(int x) {this.x = x;}public int getY() {return y;}public void setY(int y) {this.y = y;}public int getSpeed() {return speed;}public void setSpeed(int speed) {this.speed = speed;}
}

4.1.5ObserverSubMarine类

package cn.tedu.submarine;import java.util.Objects;
import java.util.Random;/*** 侦察潜艇*/
public class ObserverSubmarine {/*** 宽*/private int width;/*** 高*/private int height;/*** x轴*/private int x;/*** y轴*/private int y;/*** 速度*/private int speed;public ObserverSubmarine() {this.width = 63;this.height = 19;Random rand = new Random();x = -width;y = rand.nextInt(479-height-150+1 ) +150;this.speed = rand.nextInt(3)+1;}public ObserverSubmarine(int width, int height, int x, int y, int speed) {this.width = width;this.height = height;this.x = x;this.y = y;this.speed = speed;}/*** 侦察潜艇移动的方法*/public void move(){System.out.println("侦察潜艇移动");}@Overridepublic String toString() {return "ObserverSubmarine{" +"width=" + width +", height=" + height +", x=" + x +", y=" + y +", speed=" + speed +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;ObserverSubmarine that = (ObserverSubmarine) o;return width == that.width &&height == that.height &&x == that.x &&y == that.y &&speed == that.speed;}@Overridepublic int hashCode() {return Objects.hash(width, height, x, y, speed);}public int getWidth() {return width;}public void setWidth(int width) {this.width = width;}public int getHeight() {return height;}public void setHeight(int height) {this.height = height;}public int getX() {return x;}public void setX(int x) {this.x = x;}public int getY() {return y;}public void setY(int y) {this.y = y;}public int getSpeed() {return speed;}public void setSpeed(int speed) {this.speed = speed;}
}

4.1.6TorpedoSubmarine类

package cn.tedu.submarine;import java.util.Objects;
import java.util.Random;/*** 鱼类潜艇*/
public class TorpedoSubmarine {/*** 宽*/private int width;/*** 高*/private int height;/*** x轴*/private int x;/*** y轴*/private int y;/*** 速度*/private int speed;public TorpedoSubmarine() {this.width = 64;this.height = 20;Random rand = new Random();x = -width;y = rand.nextInt(479-height-150+1 ) +150;this.speed = rand.nextInt(3)+1;}public TorpedoSubmarine(int width, int height, int x, int y, int speed) {this.width = width;this.height = height;this.x = x;this.y = y;this.speed = speed;}/*** 鱼类潜艇移动的方法*/public void move(){System.out.println("鱼类潜艇移动");}@Overridepublic String toString() {return "TorpedoSubmarine{" +"width=" + width +", height=" + height +", x=" + x +", y=" + y +", speed=" + speed +'}';}@Overridepublic boolean equals(Object o) {if (this == o) return true;if (o == null || getClass() != o.getClass()) return false;TorpedoSubmarine that = (TorpedoSubmarine) o;return width == that.width &&height == that.height &&x == that.x &&y == that.y &&speed == that.speed;}@Overridepublic int hashCode() {return Objects.hash(width, height, x, y, speed);}public int getWidth() {return width;}public void setWidth(int width) {this.width = width;}public int getHeight() {return height;}public void setHeight(int height) {this.height = height;}public int getX() {return x;}public void setX(int x) {this.x = x;}public int getY() {return y;}public void setY(int y) {this.y = y;}public int getSpeed() {return speed;}public void setSpeed(int speed) {this.speed = speed;}
}

4.1.7World（测试类）

package cn.tedu.submarine;/*** 整个游戏世界*/
public class World {public static void main(String[] args) {Battleship s = new Battleship();ObserverSubmarine os1 = new ObserverSubmarine();ObserverSubmarine os2 = new ObserverSubmarine();ObserverSubmarine os3 = new ObserverSubmarine();ObserverSubmarine os4 = new ObserverSubmarine();TorpedoSubmarine ts1 = new TorpedoSubmarine();TorpedoSubmarine ts2 = new TorpedoSubmarine();MineSubmarine ms1 = new MineSubmarine();MineSubmarine ms2 = new MineSubmarine();Mine m1 = new Mine(ms1.getX(),ms1.getY());Mine m2 = new Mine(ms2.getX(),ms2.getY());Bomb b1 = new Bomb(s.getX(),s.getY());Bomb b2 = new Bomb(s.getX(),s.getY());System.out.println(s.toString());System.out.println(os1.toString());System.out.println(os2.toString());System.out.println(os3.toString());System.out.println(os4.toString());System.out.println(ts1.toString());System.out.println(ts2.toString());System.out.println(ms1.toString());System.out.println(ms2.toString());System.out.println(m1.toString());System.out.println(m2.toString());System.out.println(b1.toString());System.out.println(b2.toString());}
}

5.补充

成员变量和局部变量是可以同名的，但是使用的时候默认采取的是就近原则

5.1内存管理：由JVM管理

堆：new出来的对象(包括成员变量)
栈：局部变量(包括方法的参数)
方法区：------------周五再讨论

图解：

基本类型变量中装的是具体的数，引用类型变量中装的是堆中对象的地址

5.2明日单词

   1)reference:引用2)extends:继承3)super:超级4)Sea:海洋5)object:对象

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