Java Programmers Zone

                  I have faced this issue during the Java 7 upgrade from Java 6 into one of our application. You will face this issue suppose if your application or project built on lower versions of Java (in my case it is Java 1.6) and you are trying to upgrade it to the Higher versions of Java (in My case it is Java 1.7), then Eclipse will throw this error in the tool. You will face this error even after changing the compiler version from build path. To fix this issue Follow the Below Mentioned Steps. 1.  Open the ' Markers ' Tab at the bottom of the eclipse or STS tool beside the ' Properties ' Tab. (as shown in the below figure) 2. Right Click on the Error as mentioned in the below figure. in The context menu click on the ' Quick Fix ' item as shown below in the figure. 3. Select the correct Java Project Facet from the ' Quick Fix ' Window. and click on the ' Finish ' Button. 4.  After Clicking on '

The Story of the Java Platform  http://java.sun.com/nav/whatis/storyofjava.html Java Technology—An Early History  http://java.sun.com/features/1998/05/birthday.html Java Community Process   http://java.sun.com/aboutJava/communityprocess/ J2SE Platform Documentation  http://java.sun.com/docs/index.html J2EE home page  http://java.sun.com/j2ee J2EE Blueprints  http://java.sun.com/j2ee/blueprints/index.html EJB home page  http://java.sun.com/products/ejb Servlets home page  http://www.java.sun.com/products/servlet JSP home page  http://www.java.sun.com/products/jsp JDBC home page  http://www.java.sun.com/products/jdbc JMS home page  http://www.java.sun.com/products/jms JNDI home page  http://java.sun.com/products/jndi Connector home page  http://java.sun.com/j2ee/connector

• 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 measuring artificial s

                  The string concatenation operator (+) is a convenient way to combine a few strings into one. It is fine for generating a single line of output or for constructing the string representation of a small, fixed-size object, but it does not scale. Using the string concatenation operator repeatedly to concatenate n strings requires time quadratic in n. It is an unfortunate consequence of the fact that strings are immutable. When two strings are concatenated, the contents of both are copied. For example, consider the following method that constructs a string representation of a billing statement by repeatedly concatenating a line for each item: // In-appropriate use of string concatenation - Hits Performance drastically! public String statement() {      String res = "";      for (int i = 0; i < numOfItems(); i++)       res += lineOfItem(i); // String concatenation       return res; }                   This method performs very slow if the number of

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

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.

The argument list must exactly same that of the overridden method. If they don't match, you can end up with an overloaded method. The return type must be the same as, or a sub-type of, the return type declared in the original overridden method in the super-class (also called co-variant return type). Instance methods can be overridden only if they are inherited by the subclass. A subclass within the same package as the instance's super-class can override any super-class method that is not marked private or final. A subclass in a different package can override only those non-final methods marked public or protected (since protected methods are inherited by the subclass). The overriding method can throw any unchecked (run-time) exception, regardless of whether the overridden method declares the exception. The overriding method must not throw checked exceptions that are new or broader than those declared by the overridden method. For example, a method that