java - 返回 ArrayList 给出错误 : cannot find symbol

Question

我试图返回一个 ArrayList 但在最后我得到错误:找不到符号。我正在向列表中添加一些字符串和 double 并将其返回到调用它的地方。

错误:

./Sample.java:55: error: cannot find symbol
        return placeMatch;
               ^
  symbol:   variable placeMatch
  location: class Sample
1 error

考虑到有关 try catch 的内容，我将声明语句移到了顶部，我得到:

./Sample.java:54: 错误:类型不兼容 返回位置匹配； ^ 必填:字符串 找到:ArrayList

实际代码:

import java.util.ArrayList;
//...other imports

public class Sample
  extends UnicastRemoteObject
  implements SampleInterface {



    public Sample() throws RemoteException {

    }

    public String invert(String city, String state) throws RemoteException {
        try{


 ArrayList<Object> placeMatch = new ArrayList<Object>();
        // Read the existing address book.
        PlaceList place =
        PlaceList.parseFrom(new FileInputStream("places-proto.bin"));

        // Iterates though all people in the AddressBook and prints info about them.

        for (Place Placeplace: place.getPlaceList()) {
        //System.out.println("STATE: " + Placeplace.getState());
            if(Placeplace.getName().startsWith(city)){
                placeMatch.add(Placeplace.getName());
                placeMatch.add(Placeplace.getState());
                placeMatch.add(Placeplace.getLat());
                placeMatch.add(Placeplace.getLon());
                break;
            }


          }

        }catch(Exception e){
               System.out.println("opening .bin failed:" + e.getMessage());
        }
        return placeMatch;
    }

Answer 1

您需要声明:

ArrayList<Object> placeMatch = new ArrayList<Object>();

在 try block 之外。

第二个问题:

方法返回类型是String .您不能返回 ArrayList<Object> .

解决方案取决于您需要做什么。您可以更改返回类型:

public List<Object> invert(String city, String state) throws RemoteException {