Java異常、泛型與集合框架實戰：從基礎到應用

? 在Java編程的世界里，異常處理、泛型和集合框架是構建高效、健壯應用的關鍵技術。通過掌握這些技術，我們可以更好地管理程序運行時的錯誤，提高代碼的復用性和類型安全性。今天，我將通過一系列實驗，分享如何在Java中使用異常處理、泛型和集合框架來解決實際問題。

實驗背景

? Java異常處理機制允許我們優雅地處理程序運行時的錯誤，泛型提供了類型安全的集合操作，而集合框架則為我們提供了豐富的數據結構來存儲和管理數據。本次實驗的目標是通過一系列實例，掌握Java異常處理、泛型和集合框架的基本使用方法。

實驗設計

1. 驗證部分：異常處理

異常處理基礎

異常處理是Java中用于處理運行時錯誤的機制。以下是一個簡單的異常處理示例，展示如何捕獲和處理常見的異常：

public class TestExcept {public static void main(String[] args) {try {int x = 100 / 0; // ArithmeticException} catch (Exception e) {e.printStackTrace();}int[] a = new int[5];try {a[8] = 111; // ArrayIndexOutOfBoundsException} catch (Exception e) {e.printStackTrace();}int[] b = null;try {b[0] = 222; // NullPointerException} catch (Exception e) {e.printStackTrace();}Object str = "12345";try {int num = (int) str; // ClassCastException} catch (Exception e) {e.printStackTrace();}String x = "1111a";try {int n = Integer.parseInt(x); // NumberFormatException} catch (Exception e) {e.printStackTrace();}}
}

自定義異常

自定義異常類允許我們創建具有特定行為的異常。以下是一個自定義異常類的示例：

class MyExcept extends Exception {MyExcept(String info) {super(info);}
}class MyFun {void doWork(boolean isExcept) throws MyExcept {System.out.println("doWork@MyFun0");if (isExcept)throw new MyExcept("出現異常！");}
}public class TestMyExcept {public static void main(String[] args) {MyFun mf = new MyFun();try {System.out.println("開始處理...");mf.doWork(true);} catch (MyExcept e) {e.printStackTrace();System.out.println("完成異常處理！");} finally {System.out.println("完成收尾處理。");}System.out.println("結束處理。");}
}

輸出結果：

2. 驗證部分：泛型與集合框架

泛型基礎

泛型提供了類型安全的集合操作。以下是一個使用泛型的示例：

class A {public String toString() {return "A";}
}class B extends A {public String toString() {return "B";}
}class C extends B {public String toString() {return "C";}
}class MyTest<E, F> {E x;F y;MyTest(E x, F y) {this.x = x;this.y = y;}void show() {System.out.println("結果：x=" + x + "; y=" + y);}
}public class GenericClass {static void checkMyTest1(MyTest<?, ?> test) {System.out.print("測試->");test.show();}static void checkMyTest2(MyTest<? super B, ? extends B> test) {System.out.print("測試->");test.show();}public static void main(String[] args) {MyTest<String, Double> test1 = new MyTest<>("Hello!", 111.0);test1.show();MyTest<A, C> test2 = new MyTest<>(new A(), new C());test2.show();checkMyTest1(test1);checkMyTest1(test2);checkMyTest2(test2);}
}

輸出結果：

集合框架基礎

集合框架提供了豐富的數據結構來存儲和管理數據。以下是一個使用集合框架的示例：

import java.util.*;class Apple {int id;double price;Apple(int id, double price) {this.id = id;this.price = price;}public String toString() {return "apple id=" + id + "; price=" + price;}
}public class TestQueue1 {public static void main(String[] args) {Deque<Apple> queue = new ArrayDeque<>();queue.add(new Apple(6, 4.3));queue.add(new Apple(11, 5.5));queue.add(new Apple(6, 8.2));queue.addFirst(new Apple(23, 7.3));queue.removeLast();queue.add(new Apple(6, 9.6));System.out.println("隊列長度：" + queue.size());for (Apple a : queue)System.out.println(a);System.out.println("------------------");queue.pollLast();while (!queue.isEmpty())System.out.println(queue.poll());}
}

輸出結果：

3. 設計部分：綜合應用

自定義異常處理

以下是一個自定義異常處理的示例，展示如何創建和使用自定義異常類：

class MyException extends Exception {String message;public MyException(int m) {message = "溫度為" + m + "度，已超出范圍！";}public String toString() {return message;}
}class DataInput {public void check(int m) throws MyException {if (m > 500 || m < 100) {throw new MyException(m);} else {System.out.println("合理的溫度范圍。");}}
}public class TestTemperature {public static void main(String[] args) {DataInput p = new DataInput();try {p.check(1400);} catch (MyException e) {System.out.println(e.toString());}}
}

集合框架應用

以下是一個使用集合框架的示例，展示如何管理圖書信息：

import java.util.*;class Book {private String isbn;private String title;private String author;private double price;public Book(String isbn, String title, String author, double price) {this.isbn = isbn;this.title = title;this.author = author;this.price = price;}public String getIsbn() {return isbn;}public String getTitle() {return title;}public String getAuthor() {return author;}public double getPrice() {return price;}
}class BookList {private LinkedList<Book> list = new LinkedList<>();public void addBook(Book book) {list.add(book);}public void deleteBook(String isbn) {list.removeIf(book -> book.getIsbn().equals(isbn));}public Book findBookByIsbn(String isbn) {for (Book book : list) {if (book.getIsbn().equals(isbn)) {return book;}}return null;}public void updateBook(String isbn, Book newBook) {for (ListIterator<Book> it = list.listIterator(); it.hasNext();) {Book book = it.next();if (book.getIsbn().equals(isbn)) {it.set(newBook);break;}}}public Book findMostExpensiveBook() {double maxPrice = Double.MIN_VALUE;Book mostExpensiveBook = null;for (Book book : list) {if (book.getPrice() > maxPrice) {maxPrice = book.getPrice();mostExpensiveBook = book;}}return mostExpensiveBook;}
}public class TestBookStore {public static void main(String[] args) {BookList list = new BookList();list.addBook(new Book("9999", "aa", "nnn", 23.5));}
}

泛型與集合框架綜合應用

以下是一個使用泛型和集合框架的示例，展示如何管理商品信息：

import java.util.TreeSet;
import java.util.Comparator;class Product implements Comparable<Product> {private String name;private double price;public Product(String name, double price) {this.name = name;this.price = price;}public String getName() {return name;}public double getPrice() {return price;}public void setPrice(double price) {this.price = price;}@Overridepublic int compareTo(Product other) {return Double.compare(other.price, this.price);}@Overridepublic String toString() {return "Product{" +"name='" + name + '\'' +", price=" + price +'}';}
}public class ProductStore {private TreeSet<Product> products;public ProductStore() {this.products = new TreeSet<>();}public ProductStore(Comparator<? super Product> comparator) {this.products = new TreeSet<>(comparator);}public void addProduct(Product product) {products.add(product);}public void deleteProduct(Product product) {products.remove(product);}public void modifyProduct(Product oldProduct, Product newProduct) {products.remove(oldProduct);products.add(newProduct);}public void printProducts() {System.out.println("Product List:");for (Product product : products) {System.out.println(product);}}public static void main(String[] args) {ProductStore store = new ProductStore();store.addProduct(new Product("Laptop", 2000.0));store.addProduct(new Product("Smartphone", 1000.0));store.addProduct(new Product("Tablet", 1500.0));store.addProduct(new Product("Smartphone111", 1000.0));store.addProduct(new Product("Smartphone222", 1002.0));store.printProducts();Product laptop = new Product("Laptop", 1800.0);store.modifyProduct(new Product("Laptop", 2000.0), laptop);store.printProducts();store.deleteProduct(new Product("xxxx", 1000.0));store.printProducts();System.out.println("--------------------");ProductStore storeWithComparator = new ProductStore(new Comparator<Product>() {@Overridepublic int compare(Product o1, Product o2) {return Double.compare(o2.getPrice(), o1.getPrice());}});storeWithComparator.addProduct(new Product("Accessory", 50.0));storeWithComparator.addProduct(new Product("Headphones", 200.0));storeWithComparator.printProducts();}
}

輸出結果：

單詞計數器

以下是一個使用集合框架的示例，展示如何統計單詞出現的次數：

import java.util.HashMap;
import java.util.Map;
import java.util.Scanner;public class WordCounter {private Map<String, Integer> wordCounts;private Scanner scanner;public WordCounter() {wordCounts = new HashMap<>();scanner = new Scanner(System.in);}public void addWord(String word) {if (wordCounts.containsKey(word)) {wordCounts.put(word, wordCounts.get(word) + 1);} else {wordCounts.put(word, 1);}}public void printWordCounts() {for (Map.Entry<String, Integer> entry : wordCounts.entrySet()) {System.out.println(entry.getKey() + ": " + entry.getValue());}}public static void main(String[] args) {WordCounter counter = new WordCounter();System.out.println("請輸入單詞（輸入'EXIT'結束）：");String input;while (!(input = counter.scanner.nextLine()).equalsIgnoreCase("EXIT")) {counter.addWord(input);counter.printWordCounts();}counter.scanner.close();}
}

輸出結果：