Skip to main content

Posts

Showing posts from October, 2014

How To Resolve "Java compiler level does not match the version of the installed Java project facet." Issue in Eclipse, STS tool or Eclipse Based Tools

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 'Finish' button you cannot see the error. Please check the figure b…

Java Important Links

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 measuring artificial situations, such as full caches contain…

Be-Aware of the Performance of the String Concatenation...

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 items is large. To achieve acceptable performance, use a …