Methods and Classes

A class is a blueprint for objects, bundling data (fields) and behavior (methods) together, the foundation of Java's object-oriented style.

public class Student {
    private String name;
    private int xp;

    public Student(String name) {   // constructor
        this.name = name;
        this.xp = 0;
    }

    public void gainXp(int amount) {
        this.xp += amount;
    }

    public int getXp() {
        return this.xp;
    }
}

Student ada = new Student("Ada");
ada.gainXp(50);
System.out.println(ada.getXp()); // 50

• The constructor (same name as the class, no return type) runs whenever you new an instance, setting up its initial state.
• this refers to the specific instance a method was called on, needed here because the parameter name shadows the field name.
• private fields can only be accessed from inside the class itself, forcing outside code to go through methods like gainXp/getXp instead of reaching in and mutating state directly, this is encapsulation.

Why private fields plus public methods?

getXp()/gainXp() exist instead of a public xp field so the class controls how its state changes, e.g. gainXp could reject negative amounts, or trigger a level-up check, logic a bare public field could never enforce. This getter/setter pattern is one of the most common in all of Java.