Java Constructors

A constructor runs when an object is created and sets it up. It has the same name as the class and no return type. Fields are usually private, with getters and setters for access.

ExampleJava

public class Main {
  static class Person {
    private String name;
    private int age;

    Person(String name, int age) {
      this.name = name;
      this.age = age;
    }

    String getName() { return name; }
    int getAge() { return age; }
    void birthday() { age++; }
  }

  public static void main(String[] args) {
    Person p = new Person("Ada", 36);
    p.birthday();
    System.out.println(p.getName() + " is now " + p.getAge());
  }
}

Output

Ada is now 37

this refers to the current object, which is how this.name = name tells the field apart from the parameter. private keeps the data safe: outside code can only use the methods you provide.

Quick check

What does the private keyword do to a field?

Hides it from code outside the classMakes it constantMakes it faster

Finish the quick check (and any code exercise) to complete this lesson, or mark it done yourself.

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