How to implement thread-safe lazy initialization?

Question

What are some recommended approaches to achieving thread-safe lazy initialization? For instance,

// Not thread-safe
public Foo getI         


        

Answer 1

class Foo {
  private volatile Helper helper = null;
  public Helper getHelper() {
    if (helper == null) {
      synchronized(this) {
        if (helper == null) {
          helper = new Helper();
        }
      }
    }
  return helper;
}

This is called double checking! Check this http://jeremymanson.blogspot.com/2008/05/double-checked-locking.html