Packages and Access Modifiers

Real Java code is organized in packages and uses access modifiers to control who can see classes, methods, and fields. Interviewers often ask about visibility and encapsulation.

Packages

A package is a namespace. It matches folder structure: package com.froquiz.utils; means the class lives in com/froquiz/utils/. Use the package at the top of the file:

java
package com.froquiz.model;

public class User {
    private String id;
    private String name;
    // ...
}

To use a class from another package, use import: import com.froquiz.model.User; or import com.froquiz.model.*; (import all classes in that package). Classes in the same package do not need an import.

Access modifiers

Modifier	Same class	Same package	Subclass	Everywhere
private	yes	no	no	no
(default)	yes	yes	no	no
protected	yes	yes	yes	no
public	yes	yes	yes	yes

• private: Only inside the same class. Use for fields and internal helpers. Encapsulation means expose behavior via public methods, hide data.
• default (package-private): No keyword. Visible only in the same package.
• protected: Visible in the same package and in subclasses (even in another package).
• public: Visible everywhere. Use for the API you want to expose.

Encapsulation in practice

java
public class Account {
    private double balance;   // hidden

    public void deposit(double amount) {
        if (amount > 0) balance += amount;
    }

    public double getBalance() {
        return balance;
    }
}

Callers cannot set balance directly; they use deposit and getBalance. That gives you control (e.g. validation, logging) and keeps the internal representation flexible.

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