Lab: launching the streaming platform

☕ Java 17 · Writing Your First main() Method · 3/3

Goal: boot our platform with a name and a region passed on the command line, without crashing when they're missing.

Setup: in src/, create the folders com/netflix/platform/ and the file StreamingPlatform.java inside. Open a terminal in src/.

Step 1 — Package and class

package com.netflix.platform;

public class StreamingPlatform {
    private String platformName;
    private String region;
}

The two fields belong to each object. main is static, so it can't use them without an object: we'll come back to that in a later section.

Step 2 — Guard the arguments

Add main inside the class:

    public static void main(String[] args) {
        if (args.length < 2) {
            System.out.println("Usage: <name> <region>");
            return;
        }
    }

If fewer than two arguments are given, the program explains how to run it and return leaves main right away.

Step 3 — Read and print

After the if block:

        String name = args[0];   // "Netflix"
        String region = args[1]; // "France"
        System.out.println("Launching " + name + " in " + region);

+ joins the text and the values into one message.

Step 4 — Compile and run

From src/, compile with the file path and run with the full class name (package included):

$ javac com/netflix/platform/StreamingPlatform.java
$ java com.netflix.platform.StreamingPlatform Netflix France
Launching Netflix in France

Now without arguments:

$ java com.netflix.platform.StreamingPlatform
Usage: <name> <region>

No crash: the guard caught the missing arguments before args[0] was read.

Final code

package com.netflix.platform;

public class StreamingPlatform {
    private String platformName;
    private String region;

    public static void main(String[] args) {
        if (args.length < 2) {
            System.out.println("Usage: <name> <region>");
            return;
        }
        String name = args[0];   // "Netflix"
        String region = args[1]; // "France"
        System.out.println("Launching " + name + " in " + region);
    }
}

Full code on GitHub

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