According to Sun, Java language is simple because:
syntax is based on C++ (so easier for programmers to learn it after C++).
removed many confusing and/or rarely-used features e.g., explicit pointers, operator overloading etc.
No need to remove unreferenced objects because there is Automatic Garbage Collection in java.
Object-oriented means we organize our software as a combination of different types of objects that incorporates both data and behaviour.
Object-oriented programming(OOPs) is a methodology that simplify software development and maintenance by providing some rules.
Basic concepts of OOPs are:
A platform is the hardware or software environment in which a program runs.
There are two types of platforms software-based and hardware-based. Java provides software-based platform.
The Java platform differs from most other platforms in the sense that it is a software-based platform that runs on the top of other hardware-based platforms. It has two components:
Java code can be run on multiple platforms e.g. Windows, Linux, Sun Solaris, Mac/OS etc. Java code is compiled by the compiler and converted into bytecode. This bytecode is a platform-independent code because it can be run on multiple platforms i.e. Write Once and Run Anywhere(WORA).
Java is secured because:
These security are provided by java language. Some security can also be provided by application developer through SSL, JAAS, Cryptography etc.
Robust simply means strong. Java uses strong memory management. There are lack of pointers that avoids security problem. There is automatic garbage collection in java. There is exception handling and type checking mechanism in java. All these points makes java robust.
There is no implementation dependent features e.g. size of primitive types is fixed.
In C programming, int data type occupies 2 bytes of memory for 32-bit architecture and 4 bytes of memory for 64-bit architecture. But in java, it occupies 4 bytes of memory for both 32 and 64 bit architectures.
We may carry the java bytecode to any platform.
Java is faster than traditional interpretation since byte code is "close" to native code still somewhat slower than a compiled language (e.g., C++)
We can create distributed applications in java. RMI and EJB are used for creating distributed applications. We may access files by calling the methods from any machine on the internet.
A thread is like a separate program, executing concurrently. We can write Java programs that deal with many tasks at once by defining multiple threads. The main advantage of multi-threading is that it doesn't occupy memory for each thread. It shares a common memory area. Threads are important for multi-media, Web applications etc.