• The API for the J2SE provides a large library of classes that are organized into packages.
• All classes stored in the java.lang package are automatically available to all Java programs.
• To use classes that aren't in the java.lang package, you can code an import statement.
• To import one class from a package, specify the package name followed by the class name. To import all classes in a package, specify the package name followed by an asterisk (*).

import packagename.ClassName;
or
import packagename.*;

import java.text.NumberFormat;
import java.util.Scanner;
import java.util.*;
import javax.swing.*;

With an import statement

Scanner sc = new Scanner(System.in);

Without an import statement the package name is required as a qualifier

java.util.Scanner sc = new java.util.Scanner(System.in);