Asynchronous Programming Summary

CompletableFuture Concept

• Represents a future result
• Supports non-blocking operations
• Enables asynchronous programming
• Example:

  CompletableFuture<String> future = 
      CompletableFuture.supplyAsync(() -> 
          expensiveOperation());
  

Creating CompletableFuture

1. Static Factory Methods:

   // Complete future
   CompletableFuture.completedFuture(value);
   
   // Run async task
   CompletableFuture.runAsync(() -> task());
   
   // Supply async result
   CompletableFuture.supplyAsync(() -> compute());
   

2. Multiple Futures:

   CompletableFuture<Void> all = 
       CompletableFuture.allOf(future1, future2);
   
   CompletableFuture<Object> any = 
       CompletableFuture.anyOf(future1, future2);
   

Chaining Operations

1. Transformations:

   future.thenApply(x -> x * 2)        // map
         .thenCompose(x -> compute(x))  // flatMap
         .thenCombine(other, (x,y) -> x + y);
   

2. Side Effects:

   future.thenAccept(System.out::println)  // consumer
         .thenRun(() -> cleanup());        // runnable
   

Exception Handling

future.exceptionally(ex -> {
    System.err.println(ex);
    return defaultValue;
  })
  .handle((result, ex) -> {
    if (ex != null) {
      return handleError(ex);
    }
    return result;
  });

Async vs Sync Methods

1. Async Methods:

   // Executes in different thread
   future.thenApplyAsync(x -> process(x));
   future.thenComposeAsync(x -> compute(x));
   future.thenCombineAsync(other, (x,y) -> combine(x,y));
   

2. Sync Methods:

   // Executes in same thread
   future.thenApply(x -> process(x));
   future.thenCompose(x -> compute(x));
   future.thenCombine(other, (x,y) -> combine(x,y));
   

Best Practices

• Use async operations for I/O
• Handle exceptions properly
• Don't block unnecessarily
• Consider thread pools
• Chain operations efficiently
• Test async behavior
• Example: ```java CompletableFuture result = CompletableFuture.supplyAsync(() -> readFile()) .thenApplyAsync(content -> process(content)) .exceptionally(ex -> handleError(ex));