Effective Java 第一条：考虑用静态工厂方法代替构造器

平时大家常用的String类源码就是典型的静态工厂方法：

/** * Returns the string representation of the given double. */public static String valueOf(double value) {    return Double.toString(value);}/** * Returns the string representation of the given float. */public static String valueOf(float value) {    return Float.toString(value);}/** * Returns the string representation of the given int. */public static String valueOf(int value) {    return Integer.toString(value);}/** * Returns the string representation of the given long. */public static String valueOf(long value) {    return Long.toString(value);}

再如单例中的getInstance()方法。

静态工厂方法最大的优点是不用实例化类。

我们平时写类一般是这样写的：

定义一个人类，获取姓名年龄。

Man man = new Man(18,"小明");

man.getName();

man.getAge();

public class Man {    private String name;    private int age;    public Man(int age, String name) {        this.age = age;        this.name = name;    }    public int getAge() {        return age;    }    public void setAge(int age) {        this.age = age;    }    public String getName() {        return name;    }    public void setName(String name) {        this.name = name;    }}

用静态工厂方法写：

public class Man {    private String name;    private int age;    private final static Man man = new Man("小明",18);    private final static Man woman = new Man("小红",19);    private Man(String name, int age){        this.name = name;        this.age = age;    }    public static Man getMan(){        return man;    }    public static Man getWoman(){        return woman;    }    public String getName(){        return name;    }    public int getAge(){        return age;    }}

获取姓名和年龄就可以这样啦：

Man.getMan().getName()

Man.getWoman().getAge()