||Xcode is Apple's powerful integrated development environment for creating apps for Mac, iPhone, and iPad. Xcode includes the Instruments analysis tool, iOS Simulator, and the latest SDKs for iOS and OS X.
The Xcode interface seamlessly integrates code editing, UI design with Interface Builder, testing, and debugging, all within a single window. The embedded Apple LLVM compiler underlines coding mistakes as you type, and is even smart enough to fix the problems automatically.
||Objective-C is a general-purpose, object-oriented programming language primarily used for writing software for OSX and iOS. It’s a superset of the C programming language and provides object-oriented capabilities and a dynamic runtime. Objective-C inherits the syntax, primitive types, and flow control statements of C and adds syntax for defining classes and methods. It also adds language-level support for object graph management and object literals while providing dynamic typing and binding, deferring many responsibilities until runtime.
Objective-C is inherent in iOS SDK.
||Swift is a new programming language for writing iOS, OS X, watchOS, and tvOS apps that builds on the best of C and Objective-C. Swift adopts safe programming patterns and adds modern features to make programming easier, more flexible, and more secure. SWIFT is a multi-paradigm, compiled programming language created by Apple Inc. for iOS, OS X, watchOS and tvOS development. Swift is intended to be more resilient to erroneous code, with a faster compiler and new Fix-it suggestions, while being faster, more expressive and easier to understand for the developer. It also sports syntax improvements providing greater control and flow over the code and allows for interoperability with Objective-C. It is built with the LLVM compiler framework included in Xcode 6 and later and uses the Objective-C runtime, allowing C, Objective-C, C++ and Swift code to run within a single program.
Objective-C is in inherent in iOS SDK (XCode) and would be made available Open Source supporting iOS, OS X and Linux.