Java创建和销毁对象

时间： 2017/12/21 10:25:41

参考：

1. 《Effective Java》第二版

创建和销毁对象

1. 静态工厂方法，通过静态方法创建对象。

例如：

import java.util.*;

public class Human {

    //控制缓存的大小
    private final static int cacheSize = 100;
    private final static Map<String, Human> humanCache = Collections.synchronizedMap(new LinkedHashMap<>(cacheSize));

    private final String firstName;
    private final String secondName;

    private Human(String firstName, String secondName) {
        this.firstName = firstName;
        this.secondName = secondName;
    }

    public static Human valueOf(String firstName, String secondName) {
        String key = firstName + "_" + secondName;
//        showElements(humanCache);
        if (humanCache.containsKey(key)) {
            return humanCache.get(key);
        }

        Human human = new Human(firstName, secondName);
        if (humanCache.size() > cacheSize) {
            //超过缓存大小，删除最早放入的元素
            Iterator<String> iterator = humanCache.keySet().iterator();
            iterator.next();
            iterator.remove();
        }

        humanCache.put(key, human);
        return human;
    }

    private static void showElements(Map<String, Human> humanCache) {
        humanCache.keySet().forEach(key -> {
            System.out.println(humanCache.get(key));
        });
        System.out.println();
    }

    @Override
    public String toString() {
        return "Human{" +
                "firstName='" + firstName + '\'' +
                ", secondName='" + secondName + '\'' +
                '}';
    }
}

2. 当构造函数有多个参数的时候，考虑使用一个 Builder 来构建对象。

实现：

Builder接口：

public interface Builder<T> {
    public T build();
}

具体实现：

public class Person {

    enum Sex {
        MAN(true), WOMAN(false);

        public boolean value;

        Sex(boolean value) {
            this.value = value;
        }
    }

    private final String name;
    private final int age;
    private final Sex sex;
    private final String telPhone;
    private final String country;
    private final String address;

    public static class PersonBuilder implements Builder<Person> {
        //必填参数,通过构造函数指定
        private final String name;
        private final int age;
        private final Sex sex;

        //可选参数，通过方法设置
        private String telPhone;
        private String country;
        private String address;

        public PersonBuilder(String name, int age, Sex sex) {
            this.name = name;
            this.age = age;
            this.sex = sex;
        }

        public PersonBuilder telPhone(String telPhone) {
            this.telPhone = telPhone;
            return this;
        }

        public PersonBuilder country(String country) {
            this.country = country;
            return this;
        }

        public PersonBuilder address(String address) {
            this.address = address;
            return this;
        }

        @Override
        public Person build() {
            return new Person(this);
        }
    }

    public Person(PersonBuilder personBuilder) {
        this.name = personBuilder.name;
        this.age = personBuilder.age;
        this.sex = personBuilder.sex;
        this.telPhone = personBuilder.telPhone;
        this.country = personBuilder.country;
        this.address = personBuilder.address;
    }

    @Override
    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +
                ", sex=" + sex +
                ", telPhone='" + telPhone + '\'' +
                ", country='" + country + '\'' +
                ", address='" + address + '\'' +
                '}';
    }
}