List<parent> List<child> 继承解决方案
所以我正在编写我的代码并尝试将抽象工厂设计模式应用到其中。这是情况。
我有一个父类CheckList和一个子类ShoppingList。除此之外，我还有从课堂ShoppingListItem延伸出来的ListItem课程。
public abstract class CheckList {
String name;
ArrayList<ListItem> items;
public String getName() { return this.name; };
public ArrayList<ListItem> getItems() { return this.items; };
public String setName(String name) { return this.name = name; };
public abstract void addItem(String name);
public boolean editItem(String oldName, String newName) {
for (int i = 0; i < items.size(); i++)
{
if (items.get(i).getName() == oldName) {
items.get(i).setName(newName);
return true; // target found
}
}
return false; // cannot find the target
}
public boolean deleteItem(String name) {
for (int i = 0; i < items.size(); i++)
{
if (items.get(i).getName() == name) {
items.remove(i);
return true; // target found
}
}
return false; // cannot find the target
}
public boolean completeItem(String name) {
for (int i = 0; i < items.size(); i++)
{
if (items.get(i).getName() == name) {
items.get(i).setCompleted();
return true; // target found
}
}
return false; // cannot find the target
}
}
public class ShoppingList extends CheckList {
public ShoppingList (String name) {
this.name = name;
this.items = new ArrayList<ShoppingListItem>();
}
public void addItem(String name) {
// add a new ShoppingListItem to items
items.add(new ShoppingListItem(name));
}
}
我在这里遇到的问题是
ShoppingList.java:9: error: incompatible types:
ArrayList<ShoppingListItem> cannot be converted to ArrayList<ListItem>
this.items = new ArrayList<ShoppingListItem>();
看起来Java不允许在 and 之间进行这种ArrayList<parent>继承ArrayList<child>。我想知道是否有任何解决方案？我试图使ShoppingList只有一个ArrayList<ShoppingListItem>并且还继承了所有的添加/删除/等方法。这可能吗？
猛跑小猪2回答
-
jeck猫
您应该使用ArrayList<? extends ListItem>而不是ArrayList<ListItem>抽象类。也使用equals字符串比较的方法。更新您的抽象类应如下所示：abstract class CheckList<T extends ListItem> { ArrayList<T> items; ArrayList<T> getItems() { return this.items; }...实施public class ShoppingList extends CheckList<ShoppingListItem> {您应该确定您的泛型类以进行严格的类使用。完整清单：import java.util.ArrayList;abstract class CheckList<T extends ListItem> { String name; ArrayList<T> items; String getName() { return this.name; } ArrayList<T> getItems() { return this.items; } public String setName(String name) { return this.name = name; } public abstract void addItem(String name); public boolean editItem(String oldName, String newName) { for (int i = 0; i < items.size(); i++) { if (items.get(i).getName().equals(oldName)) { items.get(i).setName(newName); return true; // target found } } return false; // cannot find the target } public boolean deleteItem(String name) { for (int i = 0; i < items.size(); i++) { if (items.get(i).getName().equals(name)) { items.remove(i); return true; // target found } } return false; // cannot find the target } public boolean completeItem(String name) { for (int i = 0; i < items.size(); i++) { if (items.get(i).getName().equals(name)) { items.get(i).setCompleted(true); return true; // target found } } return false; // cannot find the target }}class ListItem { private String name; private Boolean completed; public String getName() { return name; } public Boolean getCompleted() { return completed; } public void setName(String name) { this.name = name; } public void setCompleted(Boolean completed) { this.completed = completed; }}class ShoppingListItem extends ListItem { public ShoppingListItem(String name) { this.setName(name); }}public class ShoppingList extends CheckList<ShoppingListItem> { public ShoppingList (String name) { this.name = name; this.items = new ArrayList<>(); } public void addItem(String name) { // add a new ShoppingListItem to items final ShoppingListItem item = new ShoppingListItem(name); this.items.add(item); }} -
慕后森
GenericClass<Parent>和之间没有继承关系GenericClass<Child>，但是有一个针对您的情况的解决方案，通配符：ArrayList<? extends ListItem> items = new ArrayList<>(); //list with wildcard您将能够将任何扩展的内容ListItem放入其中。还可以考虑使用 foreach 循环甚至更好的 lambda 表达式使循环更紧凑。例如你的删除方法：public boolean deleteItem(String name) { boolean removed = false; items.removeIf(item -> { item.getName().equals(name); removed = true; }); return removed;}顺便说一下，您应该将字符串与equals方法进行比较。
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相关分类
Java