OOP with Java 通知 Project 3 提交时间 3 月 29 日晚 9 点 Piazza Project 2 投票

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1 OOP with Java Yuanbin Wu

2 OOP with Java 通知 Project 3 提交时间 3 月 29 日晚 9 点 Piazza Project 2 投票

3 复习创建对象构造函数函数重载 : 函数 = 函数名 + 参数列表 public class MyType { int i; double d; char c; void set(double x) { d = x; double get() { return d; MyType(double x) { set(x); ; MyType() { System.out.println( mytype create ); ; public static void main(string [ ]args) { MyType m = new MyType(); MyType n = new MyType(2.0); public class Printer { void print(int x) { System.out.println( print an integer: + x); void print(mytype m) { System.out.println( print a MyType: + m.get());

4 复习 this 关键字在类的非静态方法中, 返回调用该方法的对象的引用销毁对象 public class MyType { int i; double d; char c; void set(double x) { this.d = x; double get() { return d; public static void main(string [ ]args) { MyType m = new MyType(); m.set(1); 垃圾回收不等于销毁对象仅回收 new 创建的内存是否回收, 何时回收由 Java 虚拟机控制.

5 OOP with Java Java 包访问控制封装

6 Java 包程序代码的组织方式表达式 a+b, x = 1, 语句 int a = 1, b = 2; 控制结构 If-else, loops 方法 ( 函数 ) 类程序库 ( 多个类 ) 包

7 Java 包包 (package) 由多个类组成这些类共享同一个名字空间 (namespace)

8 Java 包例子 :java.util 包的名字 : java.util 包含 java 提供的常用工具 java.util.linkedlist java.util.date java.util.random.

9 Java 包使用包直接使用 import 语句 import java.util.linkedlist; import java.util.date; import java.util.random; import java.util.*;

10 Java 包创建包 package 语句.java 文件首行创建文件目录结构一致 : 包的名称与文件目录结构 Let try

11 Java 包 package mypackage; public class MyType { int i; double d; char c; public void set(double x) { d = x; public double get() { return d; public MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; public static void main(string []args){ MyType m = new MyType(1, 1.0, 'a'); System.out.println(m.get()); javac mypackage/mytype.java java mypackage/mytype java mypackage.mytype

12 Java 包包结构与目录结构将 java 文件放入不同的子目录中 Let s try restaurant/ - people/ - Cook.class - Waiter.class - tools/ - Fork.class - Table.class import restaurant.people.cook; import restaurant.tools.fork; import restaurant.tools.*; import restaurant.*;

13 Java 包使用包 classpath javac, java 的参数 (-cp), CLASSPATH 环境变量指定使用包的位置 Let s try

14 Java 包类共享同一个名字空间 (namespace) 同一个包中, 类的名字不能相同不同包中, 类的名字可以相同包结构 = 目录结构例如 restaurant/ - people/ - Cook.class - Waiter.class - A.class - tools/ - Fork.class - Table.class - A.class import restaurant.people.a; import restaurant.tools.a; import restaurant.*;

15 Java 包 jar 包打包包 (packed package) 将包 ( 目录 ) 变成文件方便发布, 使用 c: create f: output to fle jar cf restaurant.jar restaurant

16 访问控制访问控制类 : 数据 + 方法公开的数据和方法提供服务所有用户都可以使用需要保持稳定, 不经常变化隐藏的数据和方法细节的, 辅助性的方法和数据不向用户公开易变

17 访问控制例子 public class Refrigerator{ Refrigerator() { open() { close() { put() { get() { enginestart() { enginesleep() { lighton() { lightof() {

18 访问控制访问控制控制类的数据 / 方法 : 是否能被访问? 能被哪些用户访问 package access public private protected

19 访问控制 package access 一个类的成员被标识为 package access 同一个包中的类可以访问其他包中的类不能访问没有标识符

20 访问控制 package access 例子 package mypackage; public class MyType { int i; double d; char c; void set(double x) { d = x; double get() { return d; MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; package mypackage; public class AnotherType { public static void main(string [ ]args){ MyType m = new MyType(1, 1.0, a ); int i = m.i; double d = m.d; char c = m.c; m.set(2); System.out.println(m.get());

21 访问控制 package access 默认包 (Default Package) //package mypackage; public class MyType { int i; double d; char c; void set(double x) { d = x; double get() { return d; MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; //package mypackage; public class AnotherType { public static void main(string [ ]args){ MyType m = new MyType(1, 1.0, a ); int i = m.i; double d = m.d; char c = m.c; m.set(2); System.out.println(m.get());

22 访问控制 package access 默认包 (default package) 如果没有 package 语句, java 默认当前目录中的 java 文件属于同一个包

23 访问控制 public 类的成员标识为 public, 则所有用户都能访问该成员 package mypackage; public class MyType { public int i; public double d; public char c; public void set(double x) { d = x; public double get() { return d; public MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; import mypackage.mytype; public class AnotherType { public static void main(string [ ]args){ MyType m = new MyType(1, 1.0, a ); int i = m.i; double d = m.d; char c = m.c; m.set(2); System.out.println(m.get());

24 访问控制 public package mypackage; public class MyType { int i; double d; char c; void set(double x) { d = x; double get() { return d; public MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; import mypackage.mytype; public class AnotherType { public static void main(string [ ]args){ MyType m = new MyType(1, 1.0, a ); int i = m.i; double d = m.d; char c = m.c; m.set(2); System.out.println(m.get());

25 访问控制 private 类的成员被标识为 private, 则除了该类自身外, 任何类不能访问改成员

26 访问控制 private package mypackage; public class MyType { private int i; private double d; private char c; private void set(double x) { d = x; private double get() { return d; public MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; public static void main(string []args){ MyType m = new MyType(1, 1.0, 'a'); m.i = 2; System.out.println(m.get()); import mypackage.mytype; public class AnotherType { public static void main(string [ ]args){ MyType m = new MyType(1, 1.0, a ); int i = m.i; double d = m.d; char c = m.c; m.set(2); System.out.println(m.get()); Access Denied!

27 访问控制 private 同一类的不同对象 class B { private int i; public B(int k) {i = k; public class A{ private int i; public A(int k) {i=k; public static void main(string args[]){ A a1 = new A(10); A a2 = new A(11); B b1 = new B(10); B b2 = new B(11); System.out.println(a1.i+a2.i); System.out.println(b1.i+b2.i);

28 访问控制 private 构造函数无法创建该类的对象 package mypackage; public class MyType { private int i; private double d; private char c; private void set(double x) { d = x; private double get() { return d; private MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; public static void main(string []args){ MyType m = new MyType(1, 1.0, 'a');

29 访问控制 private 构造函数 : 统计该类有多少对象 package mypackage; public class MyType { private int i; private double d; private char c; private void set(double x) { d = x; private double get() { return d; private MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; public static int count = 0; public static MyType makemytype(int i1, double d1, char c1){ count++; return new MyType(i1, d1, c1); import mypackage.mytype; public class AnotherType { public static void main(string [ ]args){ //MyType m = new MyType(1, 1.0, a ); MyType m = MyType.makeMyType(1, 1.0, a ); MyType n = MyType.makeMyType(1, 1.0, a ); System.out.println(MyType.count);

30 访问控制 private 构造函数 : 该类只有一个对象 package mypackage; public class MyType { private int i; private double d; private char c; public void set(double x) { d = x; public double get() { return d; private MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; private static MyType instance= null; public static MyType getinstance(){ If (instance == null) Instance = new MyType(1, 1.0, a ); return instance; import mypackage.mytype; public class AnotherType { public static void main(string [ ]args){ MyType m = MyType.getInstance(); m.set(2); MyType n = MyType.getInstance(); System.out.println(n.get()); 单件模式 (Singleton) 设计模式

31 访问控制 protected 继承 Shape draw(); erase(); move(); getcolor(); setcolor(); class Shape { private int width; private int hieght; protected int data; public void draw() { public void earse() { public void move() {. class Triangle extend Shape{ public void flipvertical() { data public void fliphorizontal() { data Triangle Circle Square flipvertical(); fliphorizontal(); draw();

32 访问控制类成员的访问控制 package access, private, public protected 类的访问控制 package access, public

33 访问控制 public class 每个.java 文件包含一个 public class 该 class 的名字等于.java 文件名 package access class 每个.java 文件中除去 public class 外, 其他的 class 为 package access

34 访问控制 package mypackage; public class MyType { int i; double d; char c; public void set(double x) { d = x; public double get() { return d; public MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; class PAClass{ public PAClass() { System.out.println( PA class ); package mypackage; public class AnotherType { public static void main(string [ ]args){ MyType m = new MyType(1, 1.0, 'a'); PAType p = new PAType();

35 MyType Revisited 访问控制 package mypackage; public class MyType { private int i; private double d; private char c; public void set(double x) { d = x; public double get() { return d; public MyType(int i1, double d1, char c1){ i = i1; d = d1; c = c1; public static void main(string []args){ MyType m = new MyType(1, 1.0, 'a'); System.out.println(m.get());

36 封装封装 (Encapsulation) 访问控制的设计 Public 提供服务, 稳定修改 public 成员将影响用户程序 Private 提供辅助, 易变修改 private 成员是安全的 Separate things that change from things that stay the same.

37 封装封装 (Encapsulation) 在满足需求的情况下, 接口尽量简单在可能的情况下尽量使用 private

38 封装 C 语言的封装 Header fle static and extern

OOP with Java 通知 Project 4: 4 月 18 日晚 9 点关于抄袭没有分数

OOP with Java Yuanbin Wu cs@ecnu OOP with Java 通知 Project 4: 4 月 18 日晚 9 点关于抄袭没有分数复习类的复用组合 (composition): has-a 关系 class MyType { public int i; public double d; public char c; public void set(double