Constructor traps

Constructor bugs are the exam's favorite class questions, because they look like working code:

Shadowing — the parameter hides the field:

private String name;
public Player(String name) {
    name = name;      // assigns the parameter to itself!
}

Fix: this.name = name;. Symptom: getters return null/0 forever.

Silent drop — the parameter never mentioned:

public Player(String n) { }   // fields stay at defaults

Wrong default thinking. Fields get Java defaults (0, null, false) BEFORE the constructor runs. A constructor that only sets half the fields silently chooses defaults for the rest — sometimes correct by luck, usually wrong.

Order of initialization: field initializers run in declaration order, then the constructor body. private int count = 3; plus a constructor assigning count = 0 ends at 0 — later assignment wins.

Static vs instance (rarely the answer, know the shape): a static field is shared by all objects (one row); instance fields are one row per object. private static int created; counts every constructor call — an exam favorite for "how many objects were made?" questions.