effective java读书笔记之第一章创建和销毁对象

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我是靠谱客的博主繁荣皮皮虾，这篇文章主要介绍effective java读书笔记之第一章创建和销毁对象，现在分享给大家，希望可以做个参考。

第一条: 考虑用静态工厂方法代替构造器
1.与构造器不同的第一大优势在于他们有名字,方便使用者调用,特别是对于参数各个不同的构造器相比,更为清楚.
2.不必在每次调用时都创建一个新的对象,可以为重复调用返回相同的对象,同时减少对象的重复创建,节省系统的开销.
3.他们可以返回原返回类型任何的子类对象,显得更灵活.
示例代码如下:

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package main.java.factory;
import java.util.Map;
import java.util.concurrent.ConcurrentHashMap;
/**
* @author Paul
* @version 0.1
* @date 2018/4/21
*/
public class Services {
//构造方法私有
private Services() {
}
private static final Map<String, Factory> providers = new ConcurrentHashMap<>();
public static final String DEFAULT_PROVIDER_NAME = "<def>";
public static void registerDefaultProvider(String name, Factory p) {
registerProvider(DEFAULT_PROVIDER_NAME, p);
}
private static void registerProvider(String defaultProviderName, Factory factory) {
providers.put(defaultProviderName, factory);
}
//用默认工厂创建服务
public static service newInstance() {
return newInstance(DEFAULT_PROVIDER_NAME);
}
//用指定工厂创建服务
public static service newInstance(String name) {
Factory factory = providers.get(name);
if (factory == null) {
throw new IllegalArgumentException("No factory registered with name" + name);
}
return factory.newService();
}
}
interface Factory {
service newService();
}
interface service {
//服务方法接口
}

它的缺点在于如果类中不含有public或者protect构造器,就无法子类化,此外静态工厂方法与类中其他静态方法实际上也没有区别,因此可能会难以区分.

第二条: 当成员变量过多时考虑用builder代替构造器
提供了javaBean模式之外的另一种构建方法,保证了线程安全同时具有良好可读性.

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package main.java.factory;
/**
* @author Paul
* @version 0.1
* @date 2018/4/22
*/
public class Student {
private final String name;
private final int age;
private final int code;
private final String clazz;
public static class Builder {
private final String name;
private final int age;
private int code = 0;
private String clazz = null;
public Builder(String name, int age) {
this.name = name;
this.age = age;
}
public Builder code(int code) {
this.code = code;
return this;
}
public Builder clazz(String clazz) {
this.clazz = clazz;
return this;
}
public Student bulid() {
return new Student(this);
}
}
public Student(Builder builder) {
name = builder.name;
age = builder.age;
code = builder.code;
clazz = builder.clazz;
}
public static void main(String[] args) {
//客户端调用
Student student=new Builder("paul", 12).code(2).clazz("一班").bulid();
}
}