Variable names in Java can start with a letter, an underscore (_), or a dollar sign ($). They cannot start with a number. After the first character, our variable names can include any letter or number. Symbols, such as %, *, @, and so on, are often reserved for operators in Java, so we should be careful when using symbols in variable names. The Java language uses the Unicode character set. The Java language is case sensitive, which means that uppercase letters are different from lowercase letters. This means that the variable X is different from the variable x, and a rose is not a Rose is not a ROSE.