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Some Important Facts About Core Java

There are 4 important OOPS concepts in Java : Inheritance, Abstraction, Encapsulation and Polymorphism. There are two types of variables in Java : Primitive types and Object Types The default value of Boolean is false (the same applies for the Wrapper class too). Marker interface is the one which doesn't contains any methods , it is like empty interface. You cannot override the 'main' method of the Java, even-though if you try to do so it will not give any exception, program compiles and executes fine. The reason is : 'main' method is of type static . Static methods are class level methods. Even-though it looks like method overriding, it is not overriding. These are two different method with respect to the corresponding class. You can Overload the 'main' method of Java, it is valid in Java. You can have only one 'Public' class and any number of non-public classes in any java source file. Inheritance is an example for IS-A relationship. C...
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Java Performance Checklist

• Specify the required performance. Ensure performance objectives are clear. Specify target response times for as much of the system as possible. Specify all variations in benchmarks, including expected response ranges (e.g., 80%  of responses for X must fall within 3 seconds). Include benchmarks for the full range of scaling expected (e.g., low to high numbers  of users, data, files, file sizes, objects, etc.). Specify and use a benchmark suite based on real user behavior. This is particularly  important for multi-user benchmarks. Agree on all target times with users, customers, managers, etc., before tuning. • Make your benchmarks long enough: over five seconds is a good target. Use elapsed time (wall-clock time) for the primary time measurements. Ensure the benchmark harness does not interfere with the performance of the  application. Run benchmarks before starting tuning, and again after each tuning exercise. Take care that you are not mea...
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Rules for Overloading the Method in Java

You can overload a method by changing its signature. method signature is made of number of arguments, type of arguments and order of arguments. Return type is not a part of method signature, so changing method return type means no overloading unless you change argument with return type. A method can be overloaded in the same class or in a subclass. if class A defines a display(float i) method, the subclass B could define a display(String s) method without overriding the super-class version that takes an int. So two methods with the same name but in different classes can still be considered overloaded, if the subclass inherits one version of the method and then declares another overloaded version in its class definition.
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