What is the difference between a field and a variable in Java?

A field (or class member) is a variable declared inside a class but outside any method, constructor, or initialization block. A field belongs either to an instance of the class (if not static) or to the class itself (if static).

A variable is a more general term. A variable is a named area of memory where data of a specific type is stored. Variables can be:

• Fields (class members)
• Local variables (declared inside a method, constructor, or block)
• Method parameters (passed to a method in its signature)

Main differences:

• Scope: Fields have a broader scope (within the class or even outside it with access modifiers), whereas local variables are only visible within the block where they are declared.
• Lifetime: Fields exist as long as the object they belong to (or as long as the class is loaded for static fields), whereas local variables only exist during the execution of the block in which they are declared.
• Default value: Fields are assigned default values (0, null, false) if not explicitly initialized. Local variables must be initialized before use.

Example:

class Example {
    int fieldVariable; // Class field, has default value 0
    static String staticField; // Static field, has default value null

    public void exampleMethod(int parameterVariable) { // parameterVariable - method parameter
        int localVariable = 10; // localVariable - local variable, must be initialized

        System.out.println(fieldVariable);
        System.out.println(parameterVariable);
        System.out.println(localVariable);
    }
}