Java异常、泛型与集合框架实战：从基础到应用

在Java编程的世界里，异常处理、泛型和集合框架是构建高效、健壮应用的关键技术。通过掌握这些技术，我们可以更好地管理程序运行时的错误，提高代码的复用性和类型安全性。今天，我将通过一系列实验，分享如何在Java中使用异常处理、泛型和集合框架来解决实际问题。

实验背景

Java异常处理机制允许我们优雅地处理程序运行时的错误，泛型提供了类型安全的集合操作，而集合框架则为我们提供了丰富的数据结构来存储和管理数据。本次实验的目标是通过一系列实例，掌握Java异常处理、泛型和集合框架的基本使用方法。

实验设计

1. 验证部分：异常处理

异常处理基础

异常处理是Java中用于处理运行时错误的机制。以下是一个简单的异常处理示例，展示如何捕获和处理常见的异常：

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();}}
}

自定义异常

自定义异常类允许我们创建具有特定行为的异常。以下是一个自定义异常类的示例：

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("出现异常！");}
}public class TestMyExcept {public static void main(String[] args) {MyFun mf = new MyFun();try {System.out.println("开始处理...");mf.doWork(true);} catch (MyExcept e) {e.printStackTrace();System.out.println("完成异常处理！");} finally {System.out.println("完成收尾处理。");}System.out.println("结束处理。");}
}

输出结果：

2. 验证部分：泛型与集合框架

泛型基础

泛型提供了类型安全的集合操作。以下是一个使用泛型的示例：

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("结果：x=" + x + "; y=" + y);}
}public class GenericClass {static void checkMyTest1(MyTest<?, ?> test) {System.out.print("测试->");test.show();}static void checkMyTest2(MyTest<? super B, ? extends B> test) {System.out.print("测试->");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);}
}

输出结果：

集合框架基础

集合框架提供了丰富的数据结构来存储和管理数据。以下是一个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("队列长度：" + queue.size());for (Apple a : queue)System.out.println(a);System.out.println("------------------");queue.pollLast();while (!queue.isEmpty())System.out.println(queue.poll());}
}

输出结果：

3. 设计部分：综合应用

自定义异常处理

以下是一个自定义异常处理的示例，展示如何创建和使用自定义异常类：

class MyException extends Exception {String message;public MyException(int m) {message = "温度为" + m + "度，已超出范围！";}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("合理的温度范围。");}}
}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());}}
}

集合框架应用

以下是一个使用集合框架的示例，展示如何管理图书信息：

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));}
}

泛型与集合框架综合应用

以下是一个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();}
}

输出结果：

单词计数器

以下是一个使用集合框架的示例，展示如何统计单词出现的次数：

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("请输入单词（输入'EXIT'结束）：");String input;while (!(input = counter.scanner.nextLine()).equalsIgnoreCase("EXIT")) {counter.addWord(input);counter.printWordCounts();}counter.scanner.close();}
}

输出结果：