java.lang.String cannot be cast to java.util.HashMap Error

Question

I have the following code trying to retrieve firebase values. My database structure is as follows:

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_mystatement);
    listview = (ListView) findViewById(R.id.listview);
    adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, list);
    listview.setAdapter(adapter);
    dref = FirebaseDatabase.getInstance().getReference();
    dref = dref.child("Dog Expenditure");

    dref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot child : dataSnapshot.getChildren()) {
                HashMap<String, Object> value = (HashMap<String, Object>) child.getValue();
                String amount = value.get("amount").toString();
                String item = value.get("item").toString();
                // This will print out amount and item
                System.out.println(amount + item);
            }
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });
}

I have tried different ways to do this but i do not just get any luck here..All i get is this error java.lang.ClassCastException: java.lang.String cannot be cast to java.util.HashMap at com.example.moses.farm.Mystatement$1.onDataChange(Mystatement.java:39) which points to this HashMap value = (HashMap) child.getValue(); line of code. I have been stuck here for almost a week, anyone with an idea of how to get this will truly help me

Not sure if this will fix it, but you should definitely not cast to a HashMap. Instead cast: Map<String, Object> value = (Map<String, Object>) child.getValue() — Frank van Puffelen
– Frank van Puffelen, Commented Mar 6, 2017 at 14:37

Anand Phadke · Accepted Answer · 2020-05-21 15:01:39Z

2

protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_mystatement);
    listview = (ListView) findViewById(R.id.listview);
    adapter = new ArrayAdapter<String>(this, android.R.layout.simple_dropdown_item_1line, list);
    listview.setAdapter(adapter);
    dref = FirebaseDatabase.getInstance().getReference();
    dref = dref.child("Dog Expenditure");

    dref.addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for (DataSnapshot child : dataSnapshot.getChildren()) {
                String amount = child.get("amount").toString();
                String item = value.get("item").toString();
                // This will print out amount and item
                System.out.println(amount + item);
            }
        }
        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });
}

use this code

edited May 21, 2020 at 15:01

user11141611

answered Mar 6, 2017 at 12:12

Anand Phadke

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3 Comments

Sir George Over a year ago

java.lang.ClassCastException: java.lang.String cannot be cast to java.util.HashMap

Sir George Over a year ago

i have noticed something very strange..in my android studio console((monitor) i see the value of a firebase entry i added manually..i.e my structurre is like this Dog Expenditure ---KeT_eEhkkiKJYOo1hb5 -- amount: "12'000" --item: "gsgag" then i manually added a child called amount: "xxxx" still under Dog Expenditure but now without this unique identifier "KeT_eEhkkiKJYOo1hb5". The console prints out xxxx. but not the original values with a unique identifire

Anand Phadke Over a year ago

ok it means at least you are able to resolve type casting error right ?

Manfred Radlwimmer · Accepted Answer · 2017-03-06 12:20:48Z

1

HashMap<String, Object> value = child.getValue();

try this one

edited Mar 6, 2017 at 12:20

Manfred Radlwimmer

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answered Mar 6, 2017 at 12:19

Karthik

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6 Comments

Sir George Over a year ago

@ManfredRadlwimmer java.lang.ClassCastException: java.lang.String cannot be cast to java.util.HashMap

Manfred Radlwimmer Over a year ago

@SirGeorge I didn't write the answer, karthi did. I simply removed the in-bowser snipped markup - can't help you with that.

Karthik Over a year ago

replace object to string

Sir George Over a year ago

@karthi java.lang.ClassCastException: java.lang.String cannot be cast to java.util.HashMap

Karthik Over a year ago

HashMap<String, String> value = (HashMap<String, String>) child.getValue();

|

Janwilx72 · Accepted Answer · 2020-05-21 20:32:26Z

1

DatabaseReference dref = FirebaseDatabase.getInstance().getReference();
dref = dref.child("Dog Expenditure");

dref.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        HashMap<String, String> value = (HashMap<String, String>) dataSnapshot.getValue();
        String amount = value.get("amount");
        String item = value.get("item");
    }
    @Override
    public void onChildChanged(DataSnapshot dataSnapshot, String s) {
    }
    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {
    }
    @Override
    public void onChildMoved(DataSnapshot dataSnapshot, String s) {
    }
    @Override
    public void onCancelled(DatabaseError databaseError) {
    }
});

edited May 21, 2020 at 20:32

user11141611

answered Mar 6, 2017 at 12:12

Janwilx72

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1 Comment

Sir George Over a year ago

please send me your retrieval code so i can try it with my app. i am strunded here

Hristo Stoyanov · Accepted Answer · 2017-03-06 12:18:51Z

0

The correct way to do it is to first create a data model:

public class DogExpenditure {
    private String amount;
    private String item;

    public String getAmount() {
        return amount;
    }

    public void setAmount(String amount) {
        this.amount = amount;
    }

    public String getItem() {
        return item;
    }

    public void setItem(String item) {
        this.item = item;
    }
}

Then add a ChildEventListener instead:

dref.addChildEventListener(new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        DogExpenditure dogExpenditure = dataSnapshot.getValue(DogExpenditure.class);
        System.out.println(dogExpenditure.getAmount()+dogExpenditure.getItem());
    }

    @Override
    public void onChildChanged(DataSnapshot dataSnapshot, String s) {

    }

    @Override
    public void onChildRemoved(DataSnapshot dataSnapshot) {

    }

    @Override
    public void onChildMoved(DataSnapshot dataSnapshot, String s) {

    }

    @Override
    public void onCancelled(DatabaseError databaseError) {

    }
});

answered Mar 6, 2017 at 12:18

Hristo Stoyanov

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1 Comment

Sir George Over a year ago

hey java.lang.ClassCastException: java.lang.String cannot be cast to java.util.HashMap errror

Kamran Ali · Accepted Answer · 2017-07-30 14:55:57Z

0

Change this line value.get("amount").toString();

TO

String.valueOf(value.get("amount")); It solved my problem.

edited Jul 30, 2017 at 14:55

answered Jul 24, 2017 at 11:26

Kamran Ali

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1 Comment

Dwhitz Over a year ago

Please format your code properly

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