In reply to UVM_LOVE:
Handle Types are
agent_a ;
uvm_agent ;
agent_b ;
agent_a ;
Am I right?
no, these are class Types which contains set of members and set of methods that operate on those members
agent_a_h,agent_b_h,temp : these are class variables where you store the class handles that references a particular class object of a particular class type
more info: A Short Class on SystemVerilog Classes - Verification Horizons