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Expertise: Beginner
Language: Java

December 11, 2003

Use Lazy Initialization to Conserve Resources

Say you have an object with a property that uses a relatively large amount of resources—and you know the property may never be accessed. Consider waiting to create the property until it's actually needed—especially if you are creating large numbers of these objects. Delaying creation in this manner is called lazy initialization.

Take for instance this Policy class:

public class Policy {
   private SalesPerson salesperson;

   // code missing to conserve space. . .

   public SalesPerson getSalesPerson() {
      return this.salesPerson;
   }
}

You could create the SalesPerson object when the Policy is created:

public Policy() {
   this.salesPerson = new SalesPerson();
}

Or you could use lazy initialization to delay the creation until the SalesPerson object is actually needed:

public Policy() {
}

public SalesPerson getSalesPerson() {
   if ( this.salesPerson == null ) {
      this.salesPerson = new SalesPerson();
   }

   return this.salesPerson;
}

Be careful when using this pattern. If you know ahead of time that the property will always be used, then lazy initialization is inappropriate because it simply adds complexity to your code. In addition, if you need your class to be thread safe, then you'll need to synchronize the test and creation of the SalesPerson object.