java面试篇之手写静态内部类实现单例

import java.util.Objects;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;

public class Singleton {
    private String name;
    private Integer id;

    private Singleton() {
    }

    @Override
    public boolean equals(Object o) {
        if (this == o) {
            return true;
        }

        if ((o == null) || (getClass() != o.getClass())) {
            return false;
        }

        Singleton singleton = (Singleton) o;

        return Objects.equals(name, singleton.name) && Objects.equals(id, singleton.id);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, id);
    }

    public static void main(String[] args) {
        ExecutorService executorService = Executors.newFixedThreadPool(5);
        final int size = 10;

        for (int i = 0; i < size; i++) {
            executorService.execute(
                    () -> {
                        System.out.println(Singleton.getInstance().hashCode());
                    });
        }
        executorService.shutdown();
    }

    private static Singleton getInstance() {
        return SingletonFactory.INSTANCE;
    }

    private static class SingletonFactory {
        private static Singleton INSTANCE = new Singleton();
    }
}