Fluent API + Singleton

/**
 * Fluent API + Singleton
 *
 * Created by yanss on 2018/9/13.
 */
public class Fluent {

    private String name;
    private int age;

    public String getName() {
        return name;
    }

    public Fluent setName(String name) {
        this.name = name;
        return this;
    }

    public int getAge() {
        return age;
    }

    public Fluent setAge(int age) {
        this.age = age;
        return this;
    }

    public static Fluent build() {
        if (instance == null) {
            synchronized (Fluent.class) {
                if (instance == null) {
                    instance = new Fluent();
                }
            }
        }
        return instance;
    }

    @Override
    public String toString() {
        return "Fluent{" + "name='" + name + '\'' + ", age=" + age + '}';
    }

    private Fluent() {}

    private static volatile Fluent instance = null;

    public static void main(String[] args) {
        Fluent.build().setName("erica").setAge(20);
        Fluent.build().setAge(21);
        System.out.println(Fluent.build());
    }

}