Error:(32, 27) error: incompatible types: Object cannot be converted to long

android, java

Solution

The problem you are having stems from the fact that `hashMap.get(item)` returns an `Object`, but your method signature specifies that you need to return a `long`.

public long getItemId(int position) {   // you say you will return a long
    String item = getItem(position);
    return hashMap.get(item);           // but try to return an Object
}

There is no way in Java for the JVM to automatically convert any random `Object` into a `long`, so the compiler is giving you that error.

There are a couple ways to fix this.

The Wrong Way

The first (bad) way is cast the variable you are getting from the map to `long` like so:

public long getItemId(int position) {   // you say you will return a long
    String item = getItem(position);
    return (long)hashMap.get(item);     // and you return a long
}

This will make your code compile, but effectively what you are doing here is promising the compiler that you are really, really sure that what you put in the `Map` is a `Long`. At this point the compiler will attempt to unbox the `Long` into a `long` and return it. If it really was a `Long` this will work, and if not you will get a `ClassCastException` thrown.

The Right Way

In newer versions of Java, there is something called Generics. Using Generics you can specify the allowed type of object which can be added to a container when you define it, like so:

// create a HashMap where all keys are Objects and all values are Longs
Map<Object, Long> hashMap = new HashMap<>();

public long getItemId(int position) {   // you say you will return a long
    String item = getItem(position);
    return hashMap.get(item);           // no cast is required
}

Now, the compiler will only allow values of type `Long` to be stored in your map, and anything you `get()` from it will automatically be a `Long`, removing the need (and danger) of casting the return type.

Problem

I am a newbie to Java. Error:(40, 5) error: method does not override or implement a method from a supertype Error:(32, 27) error: incompatible types: Object cannot be converted to long at ``` @Override public long getItemId(int position) { String item = getItem(position); return hashMap.get(item); } ``` Full code is given below ``` package com.javapapers.android.listview; import android.content.Context; import android.widget.ArrayAdapter; import java.util.HashMap; import java.util.List; public class SimpleArrayAdapter extends ArrayAdapter { Context context; int textViewResourceId; private static final String TAG = "SimpleArrayAdapter" ; HashMap hashMap = new HashMap(); public SimpleArrayAdapter(Context context, int textViewResourceId, List objects) { super(context, textViewResourceId, objects); this.context = context; this.textViewResourceId = textViewResourceId; for (int i = 0; i < objects.size(); ++i) { hashMap.put(objects.get(i), i); } } @Override public long getItemId(int position) { String item = getItem(position); return hashMap.get(item); } @Override public boolean hasStableIds() { return true; } @Override public void add(String object){ hashMap.put(object,hashMap.size()); this.notifyDataSetChanged(); } } ```

Original source