Lombok @NonNull Annotation

You can use @NonNull on the parameter of a method or constructor to have lombok generate a null-check statement for you.

Lombok has always treated any annotation named @NonNull on a field as a signal to generate a null-check if lombok generates an entire method or constructor for you, via for example @Data. Now, however, using lombok’s own @lombok.NonNull on a parameter results in the insertion of just the null-check statement inside your own method or constructor.

The null-check looks like if (param == null) throw new NullPointerException(“param”); and will be inserted at the very top of your method. For constructors, the null-check will be inserted immediately following any explicit this() or super() calls.

If a null-check is already present at the top, no additional null-check will be generated.

Note that, if a null check is already present at the top of a method or constructor, it will not be generated by lombok. Let’s consider a simple example –

class User {    @Getter @Setter @NonNull private String name;}

The above annotated code is equivalent to the following java code –

class User {    @Getter @Setter @NonNull private String name;    @NonNull    public String getName() {        return name;    }    public void setName(@NonNull final String name) {        if(name == null) throw new NullPointerException("name");        this.name = name;    }}