Java Packages & Import

Packages are folders that group related Java classes, and import lets you bring one into your file, like fetching a tool from a shelf. It keeps names organized.

In this page:

Standard Class Imports
Wildcard Package Imports
Static Imports
Using Fully Qualified Names
Implicitly Imported Packages

Syntax

java

package package.name;

import package.name.ClassName;
import package.name.*;

Standard Class Imports

A standard class import (import java.util.ArrayList;) makes one specific class available by its short name in the current file, without needing to write its fully qualified path every time it's used.

Example: Standard Class Imports

java

import java.util.ArrayList;
public class Main {
	public static void main(String[] args) {
		ArrayList<String> list = new ArrayList<>(); // short name, no full path needed
		list.add("a");
		System.out.println(list);
	}
}

Wildcard Package Imports

A wildcard import (import java.util.*;) brings in every public class from a package at once, which is convenient but can obscure exactly which classes a file actually depends on.

Example: Wildcard Package Imports

java

import java.util.*;
public class Main {
	public static void main(String[] args) {
		List<String> list = new ArrayList<>(); // brings in every public class from java.util
		list.add("a");
		System.out.println(list);
	}
}

Static Imports

A static import (import static java.lang.Math.PI;) lets you reference a class's static member directly by name (PI) instead of qualifying it every time (Math.PI), which is handy for frequently used constants or methods.

Example: Static Imports

java

import static java.lang.Math.PI;
public class Main {
	public static void main(String[] args) {
		System.out.println(PI); // no Math. prefix needed
	}
}

Using Fully Qualified Names

You can always skip importing entirely and reference a class by its fully qualified name (java.util.List<String>), which is occasionally necessary to disambiguate two classes with the same simple name from different packages.

Example: Using Fully Qualified Names

java

public class Main {
	public static void main(String[] args) {
		java.util.List<String> list = new java.util.ArrayList<>(); // no import at all
		list.add("a");
		System.out.println(list);
	}
}

Implicitly Imported Packages

Classes in java.lang (like String, Object, and System) are available in every Java file automatically without any import statement, since that package is implicitly imported everywhere.

Example: Implicitly Imported Packages

java

public class Main {
	public static void main(String[] args) {
		String s = "Hello"; // java.lang.String, no import needed
		System.out.println(s);
	}
}

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Java Packages & Import

Standard Class Imports

Wildcard Package Imports

Static Imports

Using Fully Qualified Names

Implicitly Imported Packages

Chapter Quiz — Complete all 6 topics to unlock

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