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Java Beginners’ Practical Project Troubleshooting: When execution fails, if it is an abnormal situation, an exception is thrown; otherwise, null/empty array is returned. For simple immutable data, use for loops; for streaming, filtering/transforming data sets, use Stream. Single-threaded environments use StringBuilder, and multi-threaded environments use StringBuffer. Access permission modifiers control the access scope of classes/methods/fields, which are: public (global), protected (same package), default (same package) and private (this class). Use locks to resolve race conditions and CountDownLatch to resolve deadlocks.
Java Beginner’s Confusion: Troubleshooting in Practical Projects
Introduction
For Java beginners, stepping out of the classroom and into the real world of software development can cause a lot of confusion. This article aims to solve common problems encountered by beginners in practical projects and improve their programming abilities.
1. Cancel the exception or return null/empty array?
When a method fails, should it throw an exception or return null or an empty array? The general rule is:
// 找不到数据时返回 null public User getUserById(int id) { // 从数据库查询用户 User user = null; // ... return user; } // 访问无效索引时抛出异常 public int[] getArrayElement(int[] arr, int index) { if (index < 0 || index >= arr.length) { throw new ArrayIndexOutOfBoundsException("Invalid index!"); } return arr[index]; }
2. Use Stream or for loop?
The Stream API provides efficient streaming operations, but it may be difficult for beginners to understand how it works. The rule of thumb is:
// 使用 for 循环遍历数组 int[] arr = {1, 2, 3, 4, 5}; for (int num : arr) { // 对每个元素进行操作 } // 使用 Stream 过滤和映射列表 List<Integer> numbers = Arrays.asList(1, 2, 3, 4, 5); List<Integer> evenNumbers = numbers.stream() .filter(n -> n % 2 == 0) .map(n -> n * n) .toList();
3. When to use StringBuilder/StringBuffer?
StringBuilder and StringBuffer are both mutable string buffers, but they have subtle differences:
// 在单线程环境中使用 StringBuilder StringBuilder builder = new StringBuilder(); builder.append("Hello").append(" World!"); System.out.println(builder.toString()); // 在多线程环境中使用 StringBuffer StringBuffer buffer = new StringBuffer(); buffer.append("Hello").append(" World!"); System.out.println(buffer.toString());
4. How to control access rights?
Access permission control specifies which classes/methods/fields can be accessed by other classes/objects. There are four access modifiers in Java:
// 公共类可以被所有类访问 public class MyClass { // 包保护方法可以在同一个包中访问 protected void protectedMethod() { // ... } // 私有字段只能在该类中访问 private int privateField; }
5. How to deal with parallel programming?
Parallel programming involves running code on multiple threads/cores simultaneously. Problems that beginners often encounter when using threads include:
// 使用锁解决竞态条件 Object lock = new Object(); public void synchronizedMethod() { synchronized (lock) { // ... } } // 使用 CountDownLatch 解决死锁 CountDownLatch latch = new CountDownLatch(2); public void thread1() { try { latch.await(); } catch (InterruptedException e) { // ... } }
Conclusion
These troubleshooters are designed to help Java beginners overcome common problems encountered in real-life projects. By understanding these concepts and following best practices, learners can improve their programming skills and build robust and reliable software.
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