Lazy Evaluation Summary

Lazy Evaluation Concept

• Delays computation until needed
• Avoids unnecessary calculations
• Can improve performance
• Example:

  class Lazy<T> {
    private T value;
    private boolean evaluated;
    private Producer<T> producer;
  
    public Lazy(Producer<T> producer) {
      this.producer = producer;
      this.evaluated = false;
    }
  }
  

Memoization

• Caches computed results
• Computes only once
• Reuses cached value
• Example:

  public T get() {
    if (!evaluated) {
      value = producer.produce();
      evaluated = true;
    }
    return value;
  }
  

Lazy Operations

• map: Transform value lazily
• flatMap: Chain lazy computations
• Example:

  Lazy<Integer> lazyNum = new Lazy<>(() -> expensiveComputation());
  Lazy<String> lazyStr = lazyNum.map(n -> n.toString());
  

Benefits of Lazy Evaluation

1. Performance:

   • Avoids unnecessary computations
   • Saves resources

2. Infinite Structures:

   • Can represent infinite sequences
   • Only computes needed values

3. Short-circuit Evaluation:

   • Stops when result is determined
   • Avoids redundant work

Practical Applications

• Logging systems
• Configuration loading
• Database queries
• Example:

  Lazy<String> log = new Lazy<>(() -> 
    "User " + expensiveUserLookup() + " logged in");
  
  if (debugEnabled) {
    System.out.println(log.get());  // only computed if needed
  }
  

Best Practices

• Use for expensive computations
• Implement memoization
• Consider thread safety
• Document lazy behavior
• Handle exceptions properly
• Test both lazy and eager paths