實驗十 泛型程式設計技術
實驗十 泛型程式設計技術
實驗時間 201
1、實驗目的與要求
(1) 理解泛型概念;
(2) 掌握泛型類的定義與使用;
(3) 掌握泛型方法的宣告與使用;
(4) 掌握泛型介面的定義與實現;
(5)瞭解泛型程式設計,理解其用途。
2、實驗內容和步驟
實驗1: 匯入第8章示例程式,測試程式並進行程式碼註釋。
測試程式1:
編輯、除錯、執行教材311、312頁 程式碼,結合程式執行結果理解程式;
在泛型類定義及使用程式碼處添加註釋;
掌握泛型類的定義及使用。
程式原始碼及其註釋:
Pair.java
package pair1; /** * @version 1.00 2004-05-10 * @author Cay Horstmann */ public class Pair<T> //Pair類引入了一個型別變數T,用尖括號括起來 { private T first; private T second; //指方法的返回型別以及域和區域性變數的型別 public Pair() { first = null; second = null; } public Pair(T first, T second) { this.first = first; this.second = second; } public T getFirst() { return first; } public T getSecond() { return second; } public void setFirst(T newValue) { first = newValue; } public void setSecond(T newValue) { second = newValue; } }
PairTest1.java
package pair1; /** * @version 1.01 2012-01-26 * @author Cay Horstmann */ public class PairTest1 { public static void main(String[] args) { String[] words = { "Mary", "had", "a", "little", "lamb" }; Pair<String> mm = ArrayAlg.minmax(words); System.out.println("min = " + mm.getFirst()); System.out.println("max = " + mm.getSecond()); } } class ArrayAlg { /** * Gets the minimum and maximum of an array of strings. * @param a an array of strings * @return a pair with the min and max value, or null if a is null or empty */ public static Pair<String> minmax(String[] a)//使用靜態方法來用泛型方法 { if (a == null || a.length == 0) return null; String min = a[0]; String max = a[0]; for (int i = 1; i < a.length; i++) { if (min.compareTo(a[i]) > 0) min = a[i]; if (max.compareTo(a[i]) < 0) max = a[i]; } return new Pair<>(min, max); } }
程式測試結果如下所示:
測試程式2:
編輯、除錯執行教材315頁 PairTest2,結合程式執行結果理解程式;
在泛型程式設計程式碼處新增相關注釋;
掌握泛型方法、泛型變數限定的定義及用途。
程式原始碼及其註釋:
Pair.java
package pair2; /** * @version 1.00 2004-05-10 * @author Cay Horstmann */ public class Pair<T> { private T first; private T second; public Pair() { first = null; second = null; } public Pair(T first, T second) { this.first = first; this.second = second; } public T getFirst() { return first; } public T getSecond() { return second; } public void setFirst(T newValue) { first = newValue; } public void setSecond(T newValue) { second = newValue; } }
PairTest2.java:
package pair2; import java.time.*; /** * @version 1.02 2015-06-21 * @author Cay Horstmann */ public class PairTest2 { public static void main(String[] args) { LocalDate[] birthdays = { LocalDate.of(1906, 12, 9), // G. Hopper LocalDate.of(1815, 12, 10), // A. Lovelace LocalDate.of(1903, 12, 3), // J. von Neumann LocalDate.of(1910, 6, 22), // K. Zuse }; Pair<LocalDate> mm = ArrayAlg.minmax(birthdays); System.out.println("min = " + mm.getFirst()); System.out.println("max = " + mm.getSecond()); } } class ArrayAlg { /** Gets the minimum and maximum of an array of objects of type T. @param a an array of objects of type T @return a pair with the min and max value, or null if a is null or empty */ public static <T extends Comparable> Pair<T> minmax(T[] a) { if (a == null || a.length == 0) return null; T min = a[0]; T max = a[0]; for (int i = 1; i < a.length; i++) { if (min.compareTo(a[i]) > 0) min = a[i]; if (max.compareTo(a[i]) < 0) max = a[i]; } return new Pair<>(min, max); } }
程式測試結果如下所示:
測試程式3:
用除錯執行教材335頁 PairTest3,結合程式執行結果理解程式;
瞭解萬用字元型別的定義及用途。
程式的原始碼及其註釋;
PairTest3.java:
package pair3; /** * @version 1.01 2012-01-26 * @author Cay Horstmann */ public class PairTest3 { public static void main(String[] args) { Manager ceo = new Manager("Gus Greedy", 800000, 2003, 12, 15); Manager cfo = new Manager("Sid Sneaky", 600000, 2003, 12, 15); Pair<Manager> buddies = new Pair<>(ceo, cfo); printBuddies(buddies); ceo.setBonus(1000000); cfo.setBonus(500000); Manager[] managers = { ceo, cfo }; Pair<Employee> result = new Pair<>(); minmaxBonus(managers, result); System.out.println("first: " + result.getFirst().getName() + ", second: " + result.getSecond().getName()); maxminBonus(managers, result); System.out.println("first: " + result.getFirst().getName() + ", second: " + result.getSecond().getName()); } public static void printBuddies(Pair<? extends Employee> p) //? extends type,表示帶有上界 { Employee first = p.getFirst(); Employee second = p.getSecond(); System.out.println(first.getName() + " and " + second.getName() + " are buddies."); } //"?"在這兒是萬用字元,符號表明引數的型別可以是任何一種型別,它和引數T的含義是有區別的 public static void minmaxBonus(Manager[] a, Pair<? super Manager> result) { if (a.length == 0) return; Manager min = a[0]; Manager max = a[0]; for (int i = 1; i < a.length; i++) { if (min.getBonus() > a[i].getBonus()) min = a[i]; if (max.getBonus() < a[i].getBonus()) max = a[i]; } result.setFirst(min); result.setSecond(max); } //T表示一種未知型別,而“?”表示任何一種型別 public static void maxminBonus(Manager[] a, Pair<? super Manager> result) { minmaxBonus(a, result); PairAlg.swapHelper(result); // swapHelper捕獲萬用字元型別 } // 不能寫公共靜態<T超級管理器> ... } class PairAlg { public static boolean hasNulls(Pair<?> p) { return p.getFirst() == null || p.getSecond() == null; } public static void swap(Pair<?> p) { swapHelper(p); } public static <T> void swapHelper(Pair<T> p) { T t = p.getFirst(); p.setFirst(p.getSecond()); p.setSecond(t); } }
Employee.java
package pair3; import java.time.*; public class Employee { private String name; private double salary; private LocalDate hireDay; public Employee(String name, double salary, int year, int month, int day) { this.name = name; this.salary = salary; hireDay = LocalDate.of(year, month, day); } public String getName() { return name; } public double getSalary() { return salary; } public LocalDate getHireDay() { return hireDay; } public void raiseSalary(double byPercent) { double raise = salary * byPercent / 100; salary += raise; } }
Manager.java
package pair3; public class Manager extends Employee { private double bonus; /** @param name the employee's name @param salary the salary @param year the hire year @param month the hire month @param day the hire day */ public Manager(String name, double salary, int year, int month, int day) { super(name, salary, year, month, day); bonus = 0; } public double getSalary() { double baseSalary = super.getSalary(); return baseSalary + bonus; } public void setBonus(double b) { bonus = b; } public double getBonus() { return bonus; } }
Pair.java
package pair3; /** * @version 1.00 2004-05-10 * @author Cay Horstmann */ public class Pair<T> { private T first; private T second; public Pair() { first = null; second = null; } public Pair(T first, T second) { this.first = first; this.second = second; } public T getFirst() { return first; } public T getSecond() { return second; } public void setFirst(T newValue) { first = newValue; } public void setSecond(T newValue) { second = newValue; } }
程式測試結果如下所示;
實驗2:程式設計練習:
程式設計練習1:實驗九程式設計題總結
實驗九程式設計練習1總結(從程式總體結構說明、模組說明,目前程式設計存在的困難與問題三個方面闡述)。
程式總體結構:
主要的兩個大類,有主類Main和子類Student
模組說明
在這一模組中主要講txt檔案匯入到程式,
分別用5個小類case來定義程式索要查詢的同鄉,年齡相近的人等等
Main
package Test; import java.io.BufferedReader; import java.io.File; import java.io.FileInputStream; import java.io.FileNotFoundException; import java.io.IOException; import java.io.InputStreamReader; import java.util.ArrayList; import java.util.Arrays; import java.util.Collections; import java.util.Scanner; public class Main{ private static ArrayList<Student> studentlist; public static void main(String[] args) { studentlist = new ArrayList<>(); Scanner scanner = new Scanner(System.in); File file = new File("D:\\身份證號.txt"); try { FileInputStream fis = new FileInputStream(file); BufferedReader in = new BufferedReader(new InputStreamReader(fis)); String temp = null; while ((temp = in.readLine()) != null) { Scanner linescanner = new Scanner(temp); linescanner.useDelimiter(" "); String name = linescanner.next(); String number = linescanner.next(); String sex = linescanner.next(); String age = linescanner.next(); String province =linescanner.nextLine(); Student student = new Student(); student.setName(name); student.setnumber(number); student.setsex(sex); int a = Integer.parseInt(age); student.setage(a); student.setprovince(province); studentlist.add(student); } } catch (FileNotFoundException e) { System.out.println("學生資訊檔案找不到"); e.printStackTrace(); } catch (IOException e) { System.out.println("學生資訊檔案讀取錯誤"); e.printStackTrace(); } boolean isTrue = true; while (isTrue) { System.out.println("選擇你的操作,輸入正確格式的選項"); System.out.println("a.字典排序"); System.out.println("b.輸出年齡最大和年齡最小的人"); System.out.println("c.尋找老鄉"); System.out.println("d.尋找年齡相近的人"); System.out.println("e.退出"); String m = scanner.next(); switch (m) { case "a": Collections.sort(studentlist); System.out.println(studentlist.toString()); break; case "b": int max=0,min=100; int j,k1 = 0,k2=0; for(int i=1;i<studentlist.size();i++) { j=studentlist.get(i).getage(); if(j>max) { max=j; k1=i; } if(j<min) { min=j; k2=i; } } System.out.println("年齡最大:"+studentlist.get(k1)); System.out.println("年齡最小:"+studentlist.get(k2)); break; case "c": System.out.println("老家?"); String find = scanner.next(); String place=find.substring(0,3); for (int i = 0; i <studentlist.size(); i++) { if(studentlist.get(i).getprovince().substring(1,4).equals(place)) System.out.println("老鄉"+studentlist.get(i)); } break; case "d": System.out.println("年齡:"); int yourage = scanner.nextInt(); int near=agenear(yourage); int value=yourage-studentlist.get(near).getage(); System.out.println(""+studentlist.get(near)); break; case "e": isTrue = false; System.out.println("退出程式!"); break; default: System.out.println("輸入有誤"); } } } public static int agenear(int age) { int j=0,min=53,value=0,k=0; for (int i = 0; i < studentlist.size(); i++) { value=studentlist.get(i).getage()-age; if(value<0) value=-value; if (value<min) { min=value; k=i; } } return k; } }Main
Student
package Test; public class Student implements Comparable<Student> { private String name; private String number ; private String sex ; private int age; private String province; public String getName() { return name; } public void setName(String name) { this.name = name; } public String getnumber() { return number; } public void setnumber(String number) { this.number = number; } public String getsex() { return sex ; } public void setsex(String sex ) { this.sex =sex ; } public int getage() { return age; } public void setage(int age) { // int a = Integer.parseInt(age); this.age= age; } public String getprovince() { return province; } public void setprovince(String province) { this.province=province ; } public int compareTo(Student o) { return this.name.compareTo(o.getName()); } public String toString() { return name+"\t"+sex+"\t"+age+"\t"+number+"\t"+province+"\n"; } }Student
實驗困惑:分不清在程式執行的過程中這個讀取身份證的位元組是怎麼執行的,還有就是這個程式讀取的txt檔案的內容不同的名字的位元組不會調
實驗九程式設計練習2總結(從程式總體結構說明、模組說明,目前程式設計存在的困難與問題三個方面闡述)。
程式總體結構
實驗程式主要有兩個大類,Demo類和suanfa類
模組說明
在設計四則運算的時候,首先判斷程式碼的正確性,也就是異常處理
然後進行四則運算。判斷程式碼的進一步完善
import java.io.FileNotFoundException; import java.io.PrintWriter; import java.util.Scanner; public class Demo { public static void main(String[] args) { Scanner in = new Scanner(System.in); Suanfa counter=new Suanfa(); PrintWriter out = null; try { out = new PrintWriter("text.txt"); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } int sum = 0; for (int i = 1; i <=10; i++) { int a = (int) Math.round(Math.random() * 100); int b = (int) Math.round(Math.random() * 100); int m= (int) Math.round(Math.random() * 3); switch(m) { case 0: System.out.println(i+": "+a+"/"+b+"="); while(b==0){ b = (int) Math.round(Math.random() * 100); } int c0 = in.nextInt(); out.println(a+"/"+b+"="+c0); if (c0 == counter.division(a, b)) { sum += 10; System.out.println("恭喜答案正確"); } else { System.out.println("抱歉,答案錯誤"); } break; case 1: System.out.println(i+": "+a+"*"+b+"="); int c = in.nextInt(); out.println(a+"*"+b+"="+c); if (c == counter.multiplication(a, b)) { sum += 10; System.out.println("恭喜答案正確"); } else { System.out.println("抱歉,答案錯誤"); } break; case 2: System.out.println(i+": "+a+"+"+b+"="); int c1 = in.nextInt(); out.println(a+"+"+b+"="+c1); if (c1 == counter.add(a, b)) { sum += 10; System.out.println("恭喜答案正確"); } else { System.out.println("抱歉,答案錯誤"); } break ; case 3: System.out.println(i+": "+a+"-"+b+"="); int c2 = in.nextInt(); out.println(a+"-"+b+"="+c2); if (c2 == counter.reduce(a, b)) { sum += 10; System.out.println("恭喜答案正確"); } else { System.out.println("抱歉,答案錯誤"); } break ; } } System.out.println("成績"+sum); out.println("成績:"+sum); out.close(); } }Demo
public class Suanfa { private int a; private int b; public int add(int a,int b) { return a+b; } public int reduce(int a,int b) { return a-b; } public int multiplication(int a,int b) { return a*b; } public int division(int a,int b) { if(b!=0) return a/b; else return 0; } }suanfa
實驗的困惑:
對四測運算的處理還是不夠精確,尤其是對於除法這一塊
程式設計練習2:採用泛型程式設計技術改進實驗九程式設計練習2,使之可處理實數四則運算,其他要求不變。
程式原始碼:
suanfa
public class Suanfa<T> { private T a; private T b; public Suanfa() { a = null; b = null; } public Suanfa(T a, T b) { this.a = a; this.b = b; } public int suanfa1(int a,int b) { return a+b; } public int suanfa2(int a,int b) { return a-b; } public int suanfa3(int a,int b) { return a*b; } public int suanfa4(int a,int b) { if(b!=0) return a/b; else return 0; } }
Demo:
import java.io.FileNotFoundException; import java.io.PrintWriter; import java.util.Scanner; public class Demo { public static void main(String[] args) { Scanner in = new Scanner(System.in); Suanfa counter=new Suanfa(); PrintWriter out = null; try { out = new PrintWriter("text.txt"); } catch (FileNotFoundException e) { // TODO Auto-generated catch block e.printStackTrace(); } int sum = 0; for (int i = 0; i <10; i++) { int a = (int) Math.round(Math.random() * 100); int b = (int) Math.round(Math.random() * 100); int m= (int) Math.round(Math.random() * 3); switch(m) { case 0: System.out.println(a + "+" + b + "="); int d0 = in.nextInt(); out.println(a + "+" + b + "=" + d0); if (d0 == counter.suanfa1(a, b)) { sum += 10; System.out.println("恭喜答案正確"); } else { System.out.println("抱歉,答案錯誤"); } break; case 1: while (a < b) { int x = a; a = b; b = x; } System.out.println(a + "-" + b + "="); int d1 = in.nextInt(); out.println(a + "-" + b + "=" + d1); if (d1 == counter.suanfa2(a, b)) { sum += 10; System.out.println("恭喜答案正確"); } else { System.out.println("抱歉,答案錯誤"); } break; case 2: System.out.println(a + "*" + b + "="); int d2 = in.nextInt(); out.println(a + "*" + b + "=" + d2); if (d2 ==counter.suanfa3(a, b)) { sum += 10; System.out.println("恭喜答案正確"); } else { System.out.println("抱歉,答案錯誤"); } break; case 3: while (b == 0 || a % b != 0) { a = (int) Math.round(Math.random() * 100); b = (int) Math.round(Math.random() * 100); } System.out.println(a + "/" + b + "="); int d3 = in.nextInt(); out.println(a + "/" + b + "=" + d3); if (d3 == counter.suanfa4(a, b)) { sum += 10; System.out.println("恭喜答案正確"); } else { System.out.println("抱歉,答案錯誤"); } break; } } System.out.println("成績"+sum); out.println("成績:"+sum); out.close(); } }
程式執行結果
實驗總結
本章理論知識點總結
泛型:是在定義類、介面和方法時,通過型別引數指示將要處理的物件型別
泛型程式設計:編寫程式碼可以被很多不同型別的物件所重用。
Pair類引入了一個型別變數T,用尖括號(<>)括起來,並放在類名的後面。
泛型類可以有多個型別變數。
泛型方法:
除了泛型類外,還可以只單獨定義一個方法作為泛型方法,用於指定方法引數或者返回值為泛型型別,留待方法呼叫時確定。
泛型方法可以宣告在泛型類中,也可以宣告在普通類中。
泛型變數上界的說明
NumberGeneric類所能處理的泛型變數型別需和Number有繼承關係;
extends關鍵字所宣告的上界既可以是一個類,也可以是一個介面;
<T extends Bounding Type>表示T應該是繫結型別的子型別。
泛型變數下界的說明
通過使用super關鍵字可以固定泛型引數的型別為某種型別或者其超類
當程式希望為一個方法的引數限定型別時,通常可以使用下限萬用字元
萬用字元:
“?”符號表明引數的型別可以是任何一種型別,它和引數T的含義是有區別的。T表示一種未知型別,而“?”表示任何一種型別。這種萬用字元一般有以下三種用法:
單獨的?,用於表示任何型別。
? extends type,表示帶有上界。
? super type,表示帶有下界。
通過本週的理論知識以及在實驗課的學習,我基本掌握泛型程式設計的“泛型”到底指的是什麼,我希望在以後的學習過程當中能夠越來越好。