casting type in methods in java -

-

what wrong piece of code? consider building arraylist containing buildings , building superclass farm , stonemine:

public building returnbuilding(int i) {     if(buildings.get(i) instanceof farm)         return (farm)buildings.get(i);     if(buildings.get(i) instanceof stonemine)         return (stonemine)buildings.get(i);      else         return null; }

then if call

returnbuilding(1).somemethodejustinfarmclass();

which building.get(1) instance of farm class, run time error

returnbuilding returns building, not farm. casting game.buildings.get(i) before returning not change that.

if runtime class of game.buildings.get(i) farm, cast return value of returnbuilding farm before calling somemethodejustinfarmclass method.


Popular posts from this blog

How to calculate SNR of signals in MATLAB? -

-
i've encountered simple, yet fundamental problem on calculating snr: there several signals : s1 = original , pure clean signal without noise. n1 = white gaussian noise going added s1. s2 = s1 + n1 (the noisy signal before performing noise-reduction algorithm) s3 = noise-reduced signal (after performing noise reduction algorithm) n2 = s3 - s1 (the amount of noise after performing noise-reduction algorithm) now want compare snr before , after performing noise-reduction algorithm. which signals should consider snr_before!? s1/n1 or s2/n1 ? which signals should consider snr_after!? s3/n1 or s3/n2 ? which commands or functions should use in matlab in order compute snr_before , snr_after? thanks billion putting time on helping me. what know calculating snr before : snrbeforenoise = mean( signal .^ 2 ) / mean( noise .^ 2 ); and snr after : residual_noise = signal - noise_reduced_signal; snr_after = mean( signal .^ 2 ) / mean( residual_noise .^ 2...
Read more

java - How to create Table using Apache PDFBox -

-
java - How to create Table using Apache PDFBox - we planning migrate our pdf generation utilities itext pdfbox (due licensing issues in itext). effort, able write , position text, draw lines etc. creating tables text embedded in table cells challenge, went through documentation, examples, google, stackoverflow couldn't find thing. wondering if pdfbox provides native back upwards creating tables embedded text. lastly resort utilize link https://github.com/eduardohl/paginated-pdfbox-table-sample thanks links provided tilman. using boxable api ( https://github.com/dhorions/boxable ) able create table wanted to. fyi wanted create table variable number of cells. illustration row 1 have 2 cells, row 2 have 5 cells , row 3 have 3 cells. able ease. followed example1.java in link mentioned above. java pdf pdfbox
Read more

mpi - Why is MPI_Bsend not returning error even when the buffer is insufficient to accommodate all the messages -

-
i trying implement logical ring mpi; every process receives message process id 1 less of current process , forwards next process in cyclic fashion. aim traffic buffer such loses messages or maybe puts them in out of order. cycle of communication finish when message dispatched root node comes again root. here code have tried: including relevant parts of it. if(procid!=root) { sleep(100); while(1) { tm = mpi_wtime(); mpi_irecv( &message, str_len, mpi_char, ((procid-1)>=0?(procid-1):(numproc-1)),return_data_tag, mpi_comm_world,&receiverequest); mpi_wait(&receiverequest,&status); printf("%d: received\n",procid); if(!strncmp(message,"stop",4)&&(procid==(numproc-1))) break; mpi_ssend( message, str_len, mpi_char, (procid+1)%numproc, send_data_tag, mpi_comm_world); if(!strncmp(message,"stop",4)) ...
Read more