Lab: watching the defaults

☕ Java 17 · Giving Variables Their First Value · 3/3

Goal: print the default values Java gives to fields, and see why a local variable needs a value from you.

Setup: create com/netflix/model/Movie.java under your source folder.

Step 1 — Four fields, no values

package com.netflix.model;

public class Movie {
    String title;        // → null
    double rating;       // → 0.0
    int views;           // → 0
    boolean available;   // → false
}

No = anywhere: Java fills them in when an object is created.

Step 2 — A method with a local variable

    public void displayInfo() {
        String label = "Now Showing";
        System.out.println(label + ": " + title);
    }

Try writing String label; without a value: the next line no longer compiles, with variable label might not have been initialized. Put the value back.

Step 3 — A main to print everything

    public static void main(String[] args) {
        Movie movie = new Movie();
        System.out.println("--- Default Instance Variable Values ---");
        System.out.println("Title    : " + movie.title);
        System.out.println("Rating   : " + movie.rating);
        System.out.println("Views    : " + movie.views);
        System.out.println("Available: " + movie.available);
        System.out.println("--- Calling displayInfo ---");
        movie.displayInfo();
    }

Step 4 — Run

$ javac com/netflix/model/Movie.java
$ java com.netflix.model.Movie
--- Default Instance Variable Values ---
Title    : null
Rating   : 0.0
Views    : 0
Available: false
--- Calling displayInfo ---
Now Showing: null

Every field shows its default. displayInfo() prints its local label, which you initialized, and the still-null title.

Full code on GitHub

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