复制构造函数创建依赖副本

Question

我实现了这里描述的复制构造函数.但问题仍然是当我更新时route_copy,则应用相同的更新route.所以,我不明白我的代码有什么问题？

public class Route implements Comparable<Route> {
    private List<Site> sites;

    public Route()
    {
        sites = new ArrayList<Site>();
    }

    public Route(List<Site> sites)
    {
        this.sites = sites;
    }

    /**
     * Copy constructor
     */
    public Route(Route r) {
        this(r.sites);
    }

    public void deleteSite(Site s) {
        this.sites.remove(s);
    }
}

public processData(Route route)
{
  Route route_copy = new Route(route);
  Site s = selectSite(route_copy);
  route_copy.deleteSite(s); // !!! now 'route' does not contain an  element 's'
}

Answer 1

在你的拷贝构造函数中,你只是做一个浅拷贝,而你需要做一个深拷贝:

public Route(Route r) {
    this(r.sites);
}

在这里,你仍然在复制它的引用list,它仍然指向相同的引用ArrayList.您应该修改它以创建列表的副本.可能,您还需要在arraylist中创建元素的副本,如下所示:

public Route(Route r) {
    List<Site> newSites = new ArrayList<Site>();

    for (Site obj: r.sites) {
        // Add copy of obj to the newSites
        // So you need yet another copy constructor in 'Site' class.
    }

    this.sites = newSites;
}

查看此帖子 - 浅拷贝与深拷贝.