Android : Updating an Object from different threads

I am calling 4 threads separately at a same time. These threads are making http call and fetching data from separate link. Now, I created a class, defined a single object of that class for accessing the data. All four threads are accessing the data simultaneously at a same time. Now problem is, data is not stored in synchronize manner . One threads data are being replaced by another data. How to prevent that ? How to do it in synchronize manner ? Any idea ? Please help.