@Getter(lazy=true)

Laziness is a virtue!

Overview

NEW IN Lombok 0.10: You can let lombok generate a getter which will calculate a value once, the first time this getter is called, and cache it from then on. This can be useful if calculating the value takes a lot of CPU, or the value takes a lot of memory. To use this feature, create a private final variable, initialize it with the expression that's expensive to run, and annotate your field with @Getter(lazy=true). The field will be hidden from the rest of your code, and the expression will be evaluated no more than once, when the getter is first called. There are no magic marker values (i.e. even if the result of your expensive calculation is null, the result is cached) and your expensive calculation need not be thread-safe, as lombok takes care of locking.

With Lombok

01 import lombok.Getter;
02 
03 public class GetterLazyExample {
04   @Getter(lazy=true) private final double[] cached = expensive();
05   
06   private double[] expensive() {
07     double[] result = new double[1000000];
08     for (int i = 0; i < result.length; i++) {
09       result[i] = Math.asin(i);
10     }
11     return result;
12   }
13 }

Vanilla Java

01 public class GetterLazyExample {
02   private double[] $lombok$lazy1v;
03   private volatile boolean $lombok$lazy1i;
04   private final Object $lombok$lazyLock = new Object[0];
05   
06   public double[] getCached() {
07     if (!this.$lombok$lazy1i) {
08       synchronized (this.$lombok$lazyLock) {
09         if (!this.$lombok$lazy1i) {
10           this.$lombok$lazy1v = expensive();
11           this.$lombok$lazy1i = true;
12         }
13       }
14     }
15     return this.$lombok$lazy1v;
16   }
17   
18   private double[] expensive() {
19     double[] result = new double[1000000];
20     for (int i = 0; i < result.length; i++) {
21       result[i] = Math.asin(i);
22     }
23     return result;
24   }
25 }

Small print

Lombok actually creates a few fields all prefixed with $lombok$ to cache the value. You should not rely on the exact type, name, and structure of these fields as future implementations may change them. To access the lazily initialized value, always use the generated getter.

Other Lombok annotations such as @ToString always call the getter even if you use doNotUseGetters=true.