dependencies { implementation 'com.android.support:support-core-utils:28.0.0' } import android.support.v4.util.AtomicFile; import android.support.v4.util.Pair; import android.support.v4.util.Pools; Pools.SimplePool<String> pool = new Pools.SimplePool<>(3); pool.release("Object 1"); pool.release("Object 2"); pool.release("Object 3"); String object = pool.acquire(); pool.release(null);