[英]Java - Sorting out subclass from ArrayList of superclass
我有一個ArrayList,其中包含超類的對象和一些子類的對象。 我們稱它們為subclass1和subclass2。
有沒有辦法我可以去ArrayList並辨別哪些對象是SuperClass,subclass1和subclass2。 因此,我可以將它們放入ArrayList和ArrayList中。
這是一個過於簡化的版本,但它演示了我希望做的事情。
public class food{
private String name;
public food(String name){
this.name = name;
}
}
public class pudding extends food{
public pudding(String name){
super(name);
}
}
public class breakfast extends food{
public breakfast(String name){
super(name);
}
}
public static void main(String args[]){
ArrayList<food> foods = new ArrayList();
foods.add(new food("Sausage"));
foods.add(new food("Bacon"));
foods.add(new pudding("cake"));
foods.add(new breakfast("toast"));
foods.add(new pudding("sponge"));
foods.add(new food("Rice"));
foods.add(new breakfast("eggs"));
ArrayList<pudding> puds = new ArrayList();
ArrayList<breakfast> wakeupjuices = new ArrayList();
for(food f : foods){
//if(f is pudding){puds.add(f);}
//else if(f is breakfast){wakeupjuices.add(f);}
}
}
您可以使用instanceof
關鍵字檢查所需的類型, instanceof
:
for (food f : foods)
{
if (f instanceof pudding)
puds.add(f);
else if (f instanceof breakfast)
wakeupjuices.add(f);
}
這可以通過Guava使用Multimaps.index 優雅地解決:
Function<food, String> filterFood = new Function<food, String>() {
@Override
public String apply(food input) {
if (input instanceof pudding) {
return "puddings";
}
if (input.b instanceof breakfast) {
return "breakfasts";
}
return "something else";
}
};
ImmutableListMultimap<String, food> separatedFoods = Multimaps.index(list, filterFood);
輸出將是帶有三個單獨條目的Guava Multimap ,用於:
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