Confusion for Java Beginners: Troubleshooting in Practical Projects

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:

• If the execution failure is part of a normal situation, such as data not found, return null/empty array.
• If the execution failure indicates a programming error, such as an attempt to access an invalid index, an exception is thrown.

// 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:

• For simple, immutable data, use a for loop.
• For large data sets that require streaming and filtering/transformation, use Stream.

// 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:

• StringBuilder is non-thread-safe and therefore suitable for single-threaded environments.
• StringBuffer is thread-safe and therefore suitable for multi-threaded environments.

// 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:

• public: visible to all classes/objects
• protected: visible to classes and subclasses in the same package
• default (package access): Visible to classes in the same package
• private: Visible only to the object in which the class is defined

// 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:

• Race conditions: Multiple threads access shared data at the same time, leading to unpredictable results.
• Deadlock: Two or more threads wait for each other to release resources, causing a system deadlock.

// 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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