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Background

Background. Background. 7 月 20 日. Background. 7 月 20 日. 我原以为这是平凡的一天. Background. 但我举了不该举的手. Background. 但我举了不该举的手. 说了不该说的话. Background. 但我举了不该举的手. 说了不该说的话. 听了不该听的怂恿. 这是轮子 —— Java 泛型完善. 2011 级 ACM 班 陈志鹏. Outline. Background Motivation & Criteria

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Background

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  1. Background

  2. Background 7月20日

  3. Background 7月20日 我原以为这是平凡的一天

  4. Background 但我举了不该举的手

  5. Background 但我举了不该举的手 说了不该说的话

  6. Background 但我举了不该举的手 说了不该说的话 听了不该听的怂恿

  7. 这是轮子 ——Java泛型完善 2011级ACM班 陈志鹏

  8. Outline • Background • Motivation & Criteria • Design & Implementation • One More Example • Advancement • Discussion & Conclusion • Reference

  9. Background class cat { public: void say() { printf("I am a cat.\n"); } }; class mouse { public: void say() { printf("I am a mouse.\n"); } }; template <class T> void say(T a) { a.say(); } int main() { cat acat; mouse amouse; say(acat); say(amouse); return 0; } C++

  10. Background class cat { public void say() { System.out.println ("I am a cat.\n"); } }; class mouse { public void say() { System.out.println ("I am a mouse.\n"); } }; public class example { public static <T> void say(T a) { a.say(); } Public static void main(String[] arg) { cat acat; mouse amouse; say(acat); say(amouse); return 0; } } Java

  11. Background class cat { public void say() { System.out.println ("I am a cat.\n"); } }; class mouse { public void say() { System.out.println ("I am a mouse.\n"); } }; public class example { public static <T> void say(T a) { a.say(); } Public static void main(String[] arg) { cat acat; mouse amouse; say(acat); say(amouse); return 0; } } The method say() is undefined for type T Java

  12. Background class cat { public void say() { System.out.println ("I am a cat.\n"); } }; class mouse { public void say() { System.out.println ("I am a mouse.\n"); } }; public class example { public static <T> void say(T a) { a.say(); } Public static void main(String[] arg) { cat acat; mouse amouse; say(acat); say(amouse); return 0; } } The method say() is undefined for type T Exception in thread "main" java.lang.Error: Unresolved compilation problem: The method say() is undefined for the type T Java

  13. Background class cat { public void say() { System.out.println ("I am a cat.\n"); } }; class mouse { public void say() { System.out.println ("I am a mouse.\n"); } }; public class example { public static <T> void say(T a) { a.say(); } Public static void main(String[] arg) { cat acat; mouse amouse; say(acat); say(amouse); return 0; } } Java

  14. Motivation & Criteria • 完善Java的泛型 • 基于Java • 封装与安全

  15. Design & Implementation • 所有类继承Object • 多态 • 反射

  16. Design & Implementation public static <T> void say(T a) { Class<?> demo = a.getClass(); try { Method met = demo.getMethod(“say”); met.invoke(a); } catch (Exception ex) {} } say(acat); Java

  17. One More Example class cat { public : int key; }; class mouse { public : int key; }; template <class T> boolcmp(T a, T b) { return a.key < b.key; } int main() { cat cats[100]; mouse mice[100]; //Initialization… sort(cats, cats + 100, cmp); sort(mice, mice + 100, cmp); //Output… } C++

  18. One More Example class cat { public : int key; }; class mouse { public : int key; }; template <class T> boolcmp(T a, T b) { return a.key < b.key; } int main() { cat cats[100]; mouse mice[100]; //Initialization… sort(cats, cats + 100, cmp); sort(mice, mice + 100, cmp); //Output… } error: no matching function for call to `sort(cat[100], cat*, <unknown type>)' C++

  19. One More Example class cat { public : int key; }; class mouse { public : int key; }; template <class T> boolcmp(T a, T b) { return a.key < b.key; } int main() { cat cats[100]; mouse mice[100]; //Initialization… sort(cats, cats + 100, cmp); sort(mice, mice + 100, cmp); //Output… } C++

  20. One More Example public static class comp implements Comparator{ public int compare(Object o1, Object o2) { Class<?> demo = o1.getClass; Object a = null, b = null; try { Field field = demo.getDeclaredField("key"); a = field.get(o1); b = field.get(o2); } catch (Exception ex) { } return (int)a - (int)b; }} public static void main(String[] arg) { //Initialization… Arrays.sort(cats, new comp()); //Output… } 泛型在这里 Java 那些C++做不到的事

  21. Advancement • 多参数 • 返回值 • 良好封装 • 权限修饰符 public & private • 异常处理

  22. Advancement • 多参数 • public static void say(T a, Class[] cla, Object… objs) • Method met = demo.getMethod(“…”, cla); • met.invoke(a, objs); • say(acat, new Class[] {String.class, String.class}, “Hi”, “I am a cat”) • 返回值 • 良好封装 • 权限修饰符public&private • 异常处理 Class[] cla = new Class[objs.length] cla[i] = objs[i].getClass; Java

  23. Advancement • 多参数 • 返回值 • public static int say(T a) • return met.invoke(a); • intans = say(acat); • 良好封装 • 权限修饰符public&private • 异常处理 Java

  24. Advancement 良好封装 public static <T, S> S run(T a, String method, Class[] cla, Object… objs) { Class<?> x = a.getClass(); Object ans = null; try { Method met = x.getMethod(method, cla); ans = met.invoke(a, objs); } catch (Exception ex) {} return (S) ans; } returnValue = run(acat, “say”, new Class[] {String.class, String.class}, “Hi”, “I am a cat.”); Java

  25. Advancement • 多参数 • 返回值 • 良好封装 • 权限修饰符public&private • int mo = field.getModifiers(); • String priv = Modifier.toString(mo); • int mo = met.getModifiers(); • 异常处理 Java

  26. Discussion & Conclusion • Generic Programming • 1980 Ada-> 1983 C++ • 2004jdk 1.5

  27. Discussion & Conclusion • Generic Programming • 1980 Ada -> 1983 C++ • 2004jdk 1.5 • WHY?

  28. Discussion & Conclusion • Generic Programming • 1980 Ada -> 1983 C++ • 2004JDK 1.5 & J2SE 5.0 • WHY? • No requirement • Impact of mainstream • Safety & Elegant Can be implemented by other ways Functional programming CLU

  29. Discussion & Conclusion • Generic Programming • 1980 Ada -> 1983 C++ • 2004JDK 1.5 & J2SE 5.0 • WHY? • No requirement • Impact of mainstream • Safety & Elegant • Other generic features Can be implemented by other ways Functional programming CLU ?通配符

  30. Reference • 《Java核心技术》… • Wiki…

  31. END THANKS

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