如果构建一个对象需要很多参数时，那么有三种方式可以实现。 第一种就是多重构造器

public class Person {private final int id;           //requiredprivate final String name;      //requiredprivate final int age;          //optionalprivate final int gender;          //optionalprivate final Date brithDay;          //optionalpublic Person(int id, String name, int age, int gender, Date brithDay) {this.id = id;this.name = name;this.age = age;this.gender = gender;this.brithDay = brithDay;}public Person(int id, String name, int age, int gender){this(id, name, age, gender, null);}public Person(int id, String name, int age){this(id, name, age, 0);}public Person(int id, String name){this(id, name,0);}
}
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第二种JavaBean 通过setter设置参数 缺点：因为构造过程被分到了几个调用中，在构造过程中JavaBean可能处于不一致的状态。 第三种Builder构建器模式

public class Person {private final int id;           //requiredprivate final String name;      //requiredprivate final int age;          //optionalprivate final int gender;          //optionalprivate final Date birthday;          //optionalpublic static class Builder implements com.zml.Builder<Person>{private int id;           //requiredprivate String name;      //requiredprivate int age = 0;          //optionalprivate int gender = 0;          //optionalprivate Date birthday = null;          //optionalpublic Builder(int id,String name){this.id = id;this.name = name;}public Builder age(int age){this.age = age;return this;}public Builder gender(int gender){this.gender = gender;return this;}public Builder brithDay(Date brithDay){this.birthday = brithDay;return this;}@Overridepublic Person builder() {return new Person(this);}}public Person(Builder builder) {this.id = builder.id;this.name = builder.name;this.age = builder.age;this.gender = builder.gender;this.birthday = builder.birthday;}public static void main(String[] args) {Person person = new Person.Builder(1,"hello").builder();}
}
public interface Builder<T> {T builder();
}
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