docs: public V put(K key, V value) {
          V prev_val=get(key);
          try {
              MethodCall call=new MethodCall(PUT, key, value);
              disp.callRemoteMethods(null, call, call_options);
          }
          catch(Exception e) {
              throw new RuntimeException("put(" + key + ", " + value + ") failed", e);
          }
          return prev_val;
      }