The best replacement for objective c is java.

The best alternatives to objective c are rated as following:
★★★★★  java
★★★★★  c++
★★★  cocoa
★★  xcode
★  c
★  c sharp
★  smalltalk
★  xamarin
  android java
  c programming
  java easier to learn
  if statement
  ansi c

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Speaking about objective c, one probably shouldn't forget about cocoa.

Other search terms related to objective c and their ratings are:

★★★★★ cocoa
★★★★★ c++
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objective c