Java Modifiers

Access modifiers

Access modifiers decide who is allowed to see and use a member. Choosing the right one is how you protect the inner workings of a class while still exposing the parts other code genuinely needs.

public class Account {
  public String owner;   // visible everywhere
  private double balance; // hidden from outside code

  public double getBalance() {
    return balance; // the class itself can read its private field
  }
}

Non-access modifiers

Non-access modifiers do not change visibility. Instead, they change behavior, such as whether a value can be reassigned or whether a member belongs to the class as a whole rather than to a single object.

• final: the value or method cannot be changed or overridden.
• static: the member belongs to the class, not to any one object.
• abstract: used on classes and methods that must be completed by a subclass.
• default and synchronized: mainly used with interfaces and threads in more advanced code.

public class MathHelper {
  static final double PI = 3.14159; // a shared, unchangeable constant
  static int callCount = 0;         // one counter shared by all objects

  static double circleArea(double r) {
    callCount++;
    return PI * r * r;
  }

  public static void main(String[] args) {
    System.out.println(MathHelper.circleArea(2)); // 12.56636
    System.out.println(MathHelper.callCount);     // 1
  }
}