Garbage Collection in java

One of the ideas behind Java's automatic memory management model is that programmers be spared the burden of having to perform manual memory management. In some languages like C,C++, the programmer allocates memory for the creation of objects stored on the heap and the responsibility of later deallocating that memory also resides with the programmer. If the programmer forgets to deallocate memory or writes code that fails to do so, a memory leak occurs and the program can consume an arbitrarily large amount of memory. Additionally, if the program attempts to deallocate the region of memory more than once, the result is undefined and the program may become unstable and may crash. Finally, in non garbage collected environments, there is a certain degree of overhead and complexity of user-code to track and finalize allocations. Often developers may box themselves into certain designs to provide reasonable assurances that memory leaks will not occur.

In Java, this potential problem is avoided by automatic garbage collection. The programmer determines when objects are created, and the Java runtime is responsible for managing the object's lifecycle. The program or other objects can reference an object by holding a reference to it (which, from a low-level point of view, is its address on the heap). When no references to an object remain, the Java garbage collector automatically deletes the unreachable object, freeing memory and preventing a memory leak. Memory leaks may still occur if a programmer's code holds a reference to an object that is no longer needed—in other words, they can still occur but at higher conceptual levels.

The use of garbage collection in a language can also affect programming paradigms. If, for example, the developer assumes that the cost of memory allocation/recollection is low, they may choose to more freely construct objects instead of pre-initializing, holding and reusing them. With the small cost of potential performance penalties (inner-loop construction of large/complex objects), this facilitates thread-isolation (no need to synchronize as different threads work on different object instances) and data-hiding. The use of transient immutable value-objects minimizes side-effect programming.

What is JDK &JRE???

Java Developmental Tool kit(JDK)JDK comes along with java libraries and JVM embedded in it. Apart from these it comes along with the utility tools for byte code compilation "javac", Executing the byte codes through java programmes through "java" and many more utilities found in the binary directory of java. Speaking practically JDK is essential for developers, which comes along with library packages to develop Software programmes. While JRE is minimal set of programmes which executes the java class files developed by the software developers.

Java Run Time Environment(JRE):- The java programming language adds the portability by converting the source code to byte code version which can be interpreted by the JRE and gets converted to the platform specific executable ones. Thus for different platforms one has corresponding implementation of JRE. But JRE has to meet the specification JVM (Java Virtual Machine) Concept that serves as a link between the Java libraries and the platform specific implementation of JRE. Thus JVM helps in the abstraction of inner implementation from the programmers who make use of libraries for their programmes.