Packages & API

Package groups related classes: com.rishtaara.models. First line of file: package com.rishtaara.models;

Packages — organizing classes

Package groups related classes: com.rishtaara.models. First line of file: package com.rishtaara.models;

import brings classes from other packages: import java.util.ArrayList;

Real-life example: Packages are folders in a filing cabinet — billing, HR, inventory — each drawer holds related files.

Package and import

package com.knowvora.demo;

import java.util.ArrayList;
import java.util.List;

public class App {
    public static void main(String[] args) {
        List<String> items = new ArrayList<>();
        items.add("Java");
    }
}

API — using built-in libraries

Java API is the huge library of ready classes — java.lang, java.util, java.io, java.time.

You do not rewrite ArrayList or Scanner — you import and use them.

Real-life example: API is like a toolbox in a workshop — hammer, screwdriver ready. You pick the tool, not forge metal from scratch.

java.lang — String, Math, System (auto-imported)
java.util — collections, Scanner, Random
java.io — files and streams
java.time — modern date/time