Variables are used to store data in Java. Data types define the type of data that can be stored in a variable. Operators are used to perform operations on data. Control flow statements allow programmers to control the flow of execution of a program. Methods are blocks of code that can be reused. Classes are blueprints for creating objects. Objects are instances of classes. Inheritance is the ability of one class to inherit the properties of another class. Polymorphism is the ability of an object to take on different forms. Interfaces are contracts that define the behavior of a class.