Static Keyword in Java

Static variable can be used to refer the common property of all objects.
Static variable gets memory only once in class area at the time of class loading. if any object changes the value of static variable, it will retain its value.
A static method can be invoked without the need for creating an instance of a class. Ex: className.staticMethod
Static method can only access static data member and can change the value of it.
The static method can not use non static data member or call non-static method directly.

Above content taken from http://www.javatpoint.com/static-keyword-in-java

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What is JRE?

Java Run Time Environment (JRE)   is implementation of Java Virtual Machine (JVM) that is used to interpret the byte code generated by compiling the java program

Cluster Analysis

What is Machine Learning?
Ans: Computer learns itself without explicitly programming.
For ex: Computer learns itself to recognize characters on the paper without explicitly programmed.

What is the difference between clustering and classification?
Classification is supervised learning and clustering is unsupervised learning.
Clustering can be used in outlier detection where in similar values are grouped into clusters and all the values not in any of the clusters are outliers.
Clustering can be used as data reduction technique where in cluster representation of the data are used to replace the actual data.
Clustering can be used as data discretizing technique where a numerical attribute can be discretized  by partitioning the values of attribute into clusters or groups.
You can know the distribution of data from cluster analysis.