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Reflection is a powerful feature of Java which provides the ability to inspect & modify the code at run time (manipulate internal properties of the program).
For example: It’s possible for a Java class to obtain the names of all its members and display them. Even we can also use reflection to instantiate an object, invoke it’s methods and change field values.
How it is done?
For every object JVM creates an immutable Class object which is used by reflection to get the run time properties of that object and once it has access we can change the properties. Reflection is not something which is used in daily programming tasks as it has some cons as well, one being a security threat, as using reflection we can get access to the private variables of a class and then can change it’s value.
How do we get access to the class object?
After having the access we can get the methods, variables and constructors etc.
Garbage Collection literally stops the world.
When a GC occurs in young generation space, it is completed quickly as the young generation space is small.
Young generation space is the space where newly instantiated objects are stored. Internally, this space has two survivor spaces which are used when GC occurs and the objects which still have references are shifted to a survivor space. If an object survives many cycles of GC, it is shifted to old generation space.
Problem is when GC occurs in Old generation space which contains long lived objects. This space uses a lot more memory than the young generation and when GC occurs in old generation, it literally halts all the requests made to that JVM process.
So, the world literally stops !!