JavaTutorial-SchoolofInformationSciences.ppt

Java Tutorial Write Once, Run Anywhere Java - General Java is: platform independent programming language similar to C++ in syntax similar to Smalltalk in mental paradigm Pros: also ubiquitous to net Cons: interpreted, and still under development (moving target) Java - General Java has some interesting features: automatic type checking, automatic garbage collection, simplifies pointers; no directly accessible pointer to memory, simplified network access, multi-threading! How it works…! How it works…! Java is independent only for one reason: Only depends on the Java Virtual Machine (JVM), code is compiled to bytecode, which is interpreted by the resident JVM, JIT (just in time) compilers attempt to increase speed. Java - Security Pointer denial - reduces chances of virulent programs corrupting host, Applets even more restricted - May not run local executables, Read or write to local file system, Communicate with any server other than the originating server. Object-Oriented Java supports OOD Polymorphism Inheritance Encapsulation Java programs contain nothing but definitions and instantiations of classes Everything is encapsulated in a class! Java Advantages Portable - Write Once, Run Anywhere Security has been well thought through Robust memory management Designed for network programming Multi-threaded (multiple simultaneous tasks) Dynamic extensible (loads of libraries) Classes stored in separate files Loaded only when needed Basic Java Syntax Primitive Types and Variables boolean, char, byte, short, int, long, float, double etc. These basic (or primitive) types are the only types that are not objects (due to performance issues). This means that you don’t use the new operator to create a primitive variable. Declaring primitive variables: float initVal; int retVal, index = 2; double gamma = 1.2, brightness boolean valueOk = false; Initialisation If no value is assigned prior to use, then the compiler will give an error Java sets primitive variables to zero or