question: I am optimizing a Java codebase using PMD and need two strategies to improve the code quality. Please include and highlight more than 2 specific PMD rules or techniques that address common performance issues.
answer: Optimizing a Java codebase for better performance and quality using PMD (Programming Mistake Detector) involves identifying and correcting common coding issues that can lead to inefficiencies. Here are two strategies, including specific PMD rules, to improve your code quality:
  
  ### Strategy 1: Optimize Data Structures and Collections
  Improper use of data structures can lead to performance bottlenecks. Using PMD to detect and correct these issues can significantly enhance performance.
  
  - **Avoid using inefficient data structures**: Use the `UseArrayListInsteadOfVector` rule to ensure that `ArrayList` is used in place of `Vector` when synchronization isn't required, as `ArrayList` is generally more efficient.
  - **Prefer HashMap over Hashtable**: The `UseConcurrentHashMap` rule suggests using `ConcurrentHashMap` instead of `Hashtable` for better performance and scalability when synchronization is required.
    
  By identifying places where older or less efficient collections are used, you can replace them with more modern, efficient alternatives.
  
  ### Strategy 2: Enhance Loop and String Operations
  Loops and string operations are areas where performance issues often arise due to inefficient coding practices.
  
  - **Optimize String Concatenations**: Use the `InefficientStringBuffering` rule to detect inefficient string concatenation operations using `+` in loops. Replace these with `StringBuilder` or `StringBuffer` to improve performance.
  - **Avoid empty loops**: The `EmptyStatementNotInLoop` rule helps identify empty loop bodies that execute with no effect, which can be a sign of a performance issue or a bug.
  
  By focusing on these areas, you can ensure that your code runs more efficiently, minimizing unnecessary computations and memory usage.
  
  Implementing these strategies with the highlighted PMD rules will help you optimize your Java codebase effectively.