The numbers next to the fields, methods and constructors indicate how frequently the elements are typically used.

Definition: The frequency measure is a density measure which describes the likelihood that a reference to an element in code belongs to any other Java element that occurs less frequently.

Description: Every element has a certain probability of occuring within code. The three most frequently used methods (StringBuffer.append(), String.equals() and PrintStream.println()) occur many orders of magnitudes more frequently than rarely used methods. These differences can be compressed into a more useful scale by ordering all elements according to their probability. For each element, we can then determine how many elements occur with a higher probability and how many elements occur with a lower probability. If we sum up the probability for all elements that have a lower probability, then we get the density value for the selected element. It conveniently ranges between 0% and 100%.

Thus an element that belongs to a frequency percentile of 87% is used very frequently. There are only four elements that rank in this percentile or higher (e.g. StringBuffer.append(), String.equals(), PrintStream.println() and System.out. An element that is in the frequency percentile at 2% occurs very rarely. There are more than 1400 elements in this percentile.

The frequency values are based on an in-depth analysis of more than 14 million lines of Java code.