Keywords also known as reserved words are the pre-defined identifiers reserved by Java for a specific purpose and used only in a limited, specific manner. A Keyword is that which have a special meaning those are already been explained to the java language like int, float, class, public etc these are the reserve keywords. They cannot be used as identifiers because they have special meaning within the language.
Always Remember that we can t give a name to a variable as the name of a keyword Java Provides us the 60 Keywords All the Keywords are to be written into the lower case because java is a Case Sensitive means Upper case and Lower case Letters are Different in java Some Keywords are inherit by the java language from c and C++ it adds only 27 keywords like System, Interface, abstract, final etc .
In addition to the keywords in table, there are more reserved words in Java: true, false and null. Technically they are literal values and not keywords. However, they cannot be used as identifier and they have a special meaning to the Java compiler.