In the Java programming language, a keyword is any one of 67 reserved words that have a predefined meaning in the language. Because of this, programmers cannot use keywords in some contexts, such as names for variables, methods, classes, or as any other identifier. Of these 67 keywords, 16 of them are only contextually reserved, and can sometimes be used as an identifier, unlike standard reserved words. Due to their special functions in the language, most integrated development environments for Java use syntax highlighting to display keywords in a different colour for easy identification. List of Java keywords _ Added in Java 9, the underscore has become a keyword and cannot be used as a variable name anymore. abstract A method with no definition must be declared as abstract and the class containing it must be declared as abstract. Abstract classes cannot be instantiated. Abstract methods must be implemented in the sub classes. The abstract keyword cannot be used with variables or constructors. Note that an abstract class isn't required to have an abstract method at all. assert (added in J2SE 1.4) Assert describes a predicate (a true–false statement) placed in a Java program to indicate that the developer thinks that the predicate is always true at that place. If an assertion evaluates to false at run-time, an assertion failure results, which typically causes execution to abort. Assertions are disabled at runtime by default, but can be enabled through a command-line option or programmatically through a method on the class loader. boolean Defines a boolean variable for the values "true" or "false" only. By default, the value of boolean primitive type is false. This keyword is also used to declare that a method returns a value of the primitive type boolean. break Used to end the execution in the current loop body. Used to break out of a switch block. byte The byte keyword is used to declare a field that can hold an 8-bit signed two's complement integer. This keyword is also used to declare that a method returns a value of the primitive type byte. case A statement in the switch block can be labeled with one or more case or default labels. The switch statement evaluates its expression, then executes all statements that follow the matching case label; see switch. catch Used in conjunction with a try block and an optional finally block. The statements in the