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如何说服Java构造函数接受包含其类实现特定接口的对象的列表

[英]How to convince a Java Constructor to accept a List containing objects whose Class implements a certain Interface

 原文  2015-09-16 11:56:15  2   2    java/ list/ constructor/ interface

问题描述

我目前正在对软件应用程序进行一些更改，这些更改大量使用了委托设计模式。 因此，我想相应地编写我的代码。 目前，尽管我似乎无法找到使我忙了好一阵子的问题的出路。

我当前的任务是创建某种通用的“操作类”，该类将被实现特定接口的所有对象用来对这些对象执行操作。 为了实现这一点，处理类将为任何需要更改的对象实例化此操作类的对象，并通过该操作类的对象执行其更改。

我的问题是，我无法使用接受其类实现特定接口的对象列表的构造函数来实例化“操作类”对象 。

“操作类”的构造函数如下所示（请在下面找到完整的代码示例）： 

public OperationClass(List<InterfaceName> listOfObjects) {
    super();
    listedObjects = listOfObjects;
}

它将被这样称呼： 

operationObject = new OperationClass(object.getSubObjectsList());

Eclipse会抱怨像 

"The constructor OperationClass(List<SubObjects>) is undefined."

对于我来说，这似乎有些奇怪，因为传递列表的类实现了构造方法的定义中提到的接口。 有趣的是，使用可以接受此类的单个对象的构造函数就可以了。 我的问题是：

  1. 甚至可以与接受接口列表的构造函数一起工作吗？
  2. 如何在不失去对实现接口的所有类使用代码的能力的情况下使代码工作？

注意：感谢您的反馈，修改了代码。 诀窍是将列表的数据类型更改为接口类型，并确保相应地更改Getter方法。

完整的代码示例

接口 

package test02_interfaceList;

import java.util.List;

public interface PersonI {

    public abstract String getFirstName();

    public abstract void setFirstName(String firstName);

    public abstract String getLastName();

    public abstract void setLastName(String lastName);

    public abstract List<PersonI> getSiblings();

    public abstract void setSiblings(List<PersonI> siblings);

}

实现接口的类 

package test02_interfaceList;

import java.util.List;

public class Member implements PersonI {

    private int memberId;
    private String firstName;
    private String lastName;
    private List<PersonI> siblings;

    public int getMemberId() {
        return memberId;
    }

    public void setMemberId(int memberId) {
        this.memberId = memberId;
    }

    /*
     * (non-Javadoc)
     * 
     * @see test02_interfaceList.PersonI#getFirstName()
     */
    @Override
    public String getFirstName() {
        return firstName;
    }

    /*
     * (non-Javadoc)
     * 
     * @see test02_interfaceList.PersonI#setFirstName(java.lang.String)
     */
    @Override
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    /*
     * (non-Javadoc)
     * 
     * @see test02_interfaceList.PersonI#getLastName()
     */
    @Override
    public String getLastName() {
        return lastName;
    }

    /*
     * (non-Javadoc)
     * 
     * @see test02_interfaceList.PersonI#setLastName(java.lang.String)
     */
    @Override
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    /*
     * (non-Javadoc)
     * 
     * @see test02_interfaceList.PersonI#getSiblings()
     */
    @Override
    public List<PersonI> getSiblings() {
        return siblings;
    }

    @Override
    public void setSiblings(List<PersonI> siblings) {
        this.siblings = siblings;

    }
}

通用“操作”类 

package test02_interfaceList;

import java.util.List;

public class Delegate {

    private Member currentMember;
    private List<PersonI> associatedPeople;
    private PersonI associatedPerson;

    /**
     * Standard Constructor, takes list of objects which implements the PersonI
     * interface.
     * 
     * @param listOfPeople
     */
    public Delegate(List<PersonI> listOfPeople) {
        super();
        associatedPeople = listOfPeople;
    }

    /**
     * Alternative Constructor, takes one object implementing the PersonI
     * interface.
     * 
     * @param listOfPeople
     */
    public Delegate(PersonI person) {
        super();
        associatedPerson = person;
    }

    public void addToAssocPeopleList(PersonI person) {
        System.out.println("Adding " + person.getFirstName() + " to list of associated people.");
        associatedPeople.add(person);
    }

    public void removeFromAssocPeopleList(PersonI person) {
        System.out.println("Removing " + person.getFirstName() + " from list of associated people.");
        associatedPeople.remove(person);
    }

    public Member getCurrentMember() {
        return currentMember;
    }

    public void setCurrentMember(Member currentMember) {
        this.currentMember = currentMember;
    }

    public List<PersonI> getAssociatedPeople() {
        return associatedPeople;
    }

    public void setAssociatedPeople(List<PersonI> associatedPeople) {
        this.associatedPeople = associatedPeople;
    }

    public PersonI getAssociatedPerson() {
        return associatedPerson;
    }

    public void setAssociatedPerson(PersonI associatedPerson) {
        this.associatedPerson = associatedPerson;
    }

}

使用main（）方法的类 

import java.util.ArrayList;
import java.util.List;

public class Main {

    public static void main(String[] args) {
        // Main Method

        Delegate member01Operations;
        List<PersonI> siblings = new ArrayList<PersonI>();

        Member member01 = new Member();
        member01.setMemberId(42);
        member01.setFirstName("John");
        member01.setLastName("Doe");
        member01.setSiblings(siblings);

        Member member02 = new Member();
        member02.setMemberId(43);
        member02.setFirstName("Joanna");
        member02.setLastName("Doe");

        Member member03 = new Member();
        member03.setMemberId(43);
        member03.setFirstName("James");
        member03.setLastName("Doe");

        // The constructor now accepts the returned list as it contains the
        // PersonI interface datatype
        member01Operations = new Delegate(member01.getSiblings());

        member01Operations.addToAssocPeopleList(member02);
        member01Operations.addToAssocPeopleList(member03);

        for (PersonI person : member01Operations.getAssociatedPeople()) {
            System.out.println(person.getFirstName());
        }
    }
}

2 个解决方案

解决方案1
 3 已采纳  2015-09-16 11:58:53

您应该了解List<SubObjects>不是List<InterfaceName>的子类，因此您不能在需要List<InterfaceName>地方传递List<SubObjects> 。

您应该更改getSubObjectsList()以返回List<InterfaceName>而不是List<SubObjects> 。 无论如何，通常最好在变量和方法参数中使用接口类型而不是类类型。

解决方案2
 1  2015-09-16 12:10:25

我已经更改了代码。请尝试如下使用。 

package test02_interfaceList;

import java.util.ArrayList;
import java.util.List;

public class Delegate {

    private Member currentMember;
    private List<PersonI<?>> associatedPeople = new ArrayList<PersonI<?>>();
    private PersonI<?> associatedPerson;

    /**
     * Standard Constructor, takes list of objects which implements the PersonI
     * interface.
     * 
     * @param listOfPeople
     */
    public Delegate(List<? extends PersonI<?>> listOfPeople) {
        super();
        for (PersonI<?> personI : listOfPeople) {
            associatedPeople.add(personI);
        }

    }

    /**
     * Alternative Constructor, takes one object implementing the PersonI
     * interface.
     * 
     * @param listOfPeople
     */
    public Delegate(PersonI<?> person) {
        super();
        associatedPerson = person;
    }

    public void addToAssocPeopleList(PersonI<?> person) {
        System.out.println("Adding " + person.getFirstName() + " to list of associated people.");
        associatedPeople.add(person);
    }

    public void removeFromAssocPeopleList(PersonI<?> person) {
        System.out.println("Removing " + person.getFirstName() + " from list of associated people.");
        associatedPeople.remove(person);
    }

    public Member getCurrentMember() {
        return currentMember;
    }

    public void setCurrentMember(Member currentMember) {
        this.currentMember = currentMember;
    }

    public List<? extends PersonI<?>> getAssociatedPeople() {
        return associatedPeople;
    }

    public void setAssociatedPeople(List<PersonI<?>> associatedPeople) {
        this.associatedPeople = associatedPeople;
    }

    public PersonI<?> getAssociatedPerson() {
        return associatedPerson;
    }

    public void setAssociatedPerson(PersonI<?> associatedPerson) {
        this.associatedPerson = associatedPerson;
    }

}

会员等级： 

package test02_interfaceList;

import java.util.List;

public class Member implements PersonI<Member> {

    private int memberId;
    private String firstName;
    private String lastName;
    private List<Member> siblings;

    public int getMemberId() {
        return memberId;
    }

    public void setMemberId(int memberId) {
        this.memberId = memberId;
    }

    /* (non-Javadoc)
     * @see test02_interfaceList.PersonI#getFirstName()
     */
    @Override
    public String getFirstName() {
        return firstName;
    }

    /* (non-Javadoc)
     * @see test02_interfaceList.PersonI#setFirstName(java.lang.String)
     */
    @Override
    public void setFirstName(String firstName) {
        this.firstName = firstName;
    }

    /* (non-Javadoc)
     * @see test02_interfaceList.PersonI#getLastName()
     */
    @Override
    public String getLastName() {
        return lastName;
    }

    /* (non-Javadoc)
     * @see test02_interfaceList.PersonI#setLastName(java.lang.String)
     */
    @Override
    public void setLastName(String lastName) {
        this.lastName = lastName;
    }

    /* (non-Javadoc)
     * @see test02_interfaceList.PersonI#getSiblings()
     */
    @Override
    public List<Member> getSiblings() {
        return siblings;
    }

    /* (non-Javadoc)
     * @see test02_interfaceList.PersonI#setSiblings(java.util.List)
     */
    @Override
    public void setSiblings(List<Member> siblings) {
        this.siblings = siblings;
    }

}

人机界面 

package test02_interfaceList;

import java.util.List;

public interface PersonI<T extends PersonI> {

    public abstract String getFirstName();

    public abstract void setFirstName(String firstName);

    public abstract String getLastName();

    public abstract void setLastName(String lastName);

    public abstract List<T> getSiblings();

    public abstract void setSiblings(List<T> siblings);

}

主类： 

package test02_interfaceList;

    public class Main {

        public static void main(String[] args) {
            // Main Method

            Delegate peopleOperations;

            Member member01 = new Member();
            member01.setMemberId(42);
            member01.setFirstName("John");
            member01.setLastName("Doe");

            Member member02 = new Member();
            member01.setMemberId(43);
            member01.setFirstName("Joanna");
            member01.setLastName("Doe");

            member01.getSiblings().add(member02);
            member02.getSiblings().add(member01);

            // This works
            peopleOperations = new Delegate(member01);

            // This doesn't ('Constructor(List<Member>) undefined') - why? Class
            // Member implements the PersonI interface!
            peopleOperations = new Delegate(member01.getSiblings());

        }

    }

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