功能未扩展到其他类别

Question

I've got a class full of getters and setters, so I can make a list of watches and have it accessible to the rest of my app:

Watch.java:

 public class Watch { private String brand, mvmt, serial, urlLoc; private int wr, year; private double price; //getters and setters } 

I want to use this to get a list:

 package com.example.pat.watchproj; import java.util.LinkedList; public class WatchList extends LinkedList { //set up the watch list so it can be accessed through the app private static WatchList wlInst = new WatchList(); public static WatchList getInstance(){ if(wlInst == null){ wlInst = new WatchList(); } return wlInst; } private WatchList(){ } public static void setInstance(WatchList watchList){ wlInst = watchList; } } 

Here is an example of how I'd add a watch

public void addWatch(View view){
    //initilize watch list and all edit texts
    //will need to parsedouble and parseinteger
    watchList = WatchList.getInstance();
    Watch usrWatch = new Watch();
    EditText addBrand = (EditText) findViewById(R.id.addBrand);
    EditText addSerial = (EditText) findViewById(R.id.addSerial);
    EditText addMvmt = (EditText) findViewById(R.id.addMvmt);
    EditText addWr = (EditText) findViewById(R.id.addWr);
    EditText addYear = (EditText) findViewById(R.id.addYear);
    EditText addPrice = (EditText) findViewById(R.id.addPrice);
    EditText addUrl = (EditText) findViewById(R.id.addUrl);

    //add to object now
    usrWatch.setBrand(addBrand.getText().toString());
    usrWatch.setMvmt(addMvmt.getText().toString());
    usrWatch.setSerial(addSerial.getText().toString());
    usrWatch.setWr(Integer.parseInt(addWr.getText().toString()));
    usrWatch.setPrice(Double.parseDouble(addPrice.getText().toString()));
    usrWatch.setYear(Integer.parseInt(addYear.getText().toString()));
    usrWatch.setUrlLoc(addUrl.getText().toString());

    watchList.add(usrWatch);
    WatchList.setInstance(watchList);

    Toast.makeText(addWatch.this, "Watch added", Toast.LENGTH_SHORT).show();
}

So, in mainactivity, when I write this:

public void onOption8 (MenuItem i){
    //show most expensive
    WatchList watchList = WatchList.getInstance();
    int x = 0;
    for(int a = 0; a < watchList.size(); a++) {
        if (watchList.get(x).getPrice() <  watchList.get(a).getPrice()) {
            x = a;

        }
    }
}

So after that runs, I should be able to use watchList.get(x).getSerial() to get the serial of the most expensive watch. But android studio is telling me that it cant resolve method getPrice in onOption8, and I'm not sure where I'm going wrong. Let me know if I'm not being clear/can provide more info. Thanks

Answer 1

You haven't provided a type for your custom LinkedList implementation; as such get(x) is returning an Object . Change the WatchList class declaration to:

public class WatchList extends LinkedList<Watch> {
    ...
}

Answer 2

This error probably occurs because you havn't given the WatchList class a type parameter yet. In the onOption8, the compiler doesn't know whether the WatchList you received is type < String >, < Car >, or < Watch >.

Make sure that you either just create a LinkedList of type Watch, like so

LinkedList<Watch> ll = new LinkedList<Watch>() 

or that you specify that WatchList is in fact a LinkedList of Watch objects, and not of anything else, in your WatchList class.