What is the significance of each access modifier in Java?

In Java, there are four main access modifiers that determine the visibility level of classes, methods, and fields:

• public — accessible from anywhere, from any class.
• protected — accessible within its own class, subclasses, and classes in the same package.
• (default) package-private — if no modifier is specified, accessible only within the package.
• private — accessible only within its own class.

Example:

public class Example {
    public int publicField;       // accessible everywhere
    protected int protectedField; // accessible in class, subclasses, and package
    int defaultField;             // accessible only within the package
    private int privateField;     // accessible only within the class
}

These modifiers help encapsulate data and control which parts of the code can interact with certain elements, which is important for security and maintainability of the code.