Using Imported Classes

Estimated time to read: 2 minutes

Overview¶

When a class has been imported its name can be used without the qualification.

In this example, Date is resolved to java.util.Date at compilation time.

package io.entityfour;

import java.util.Date;

public class DatePrinter(){
 public void printDate(Date aDate) {
  System.out.println(aDate.toString());
 }
}

Class Name Table¶

The Name Table below is an example of classes used within the Car class that has been generated throughout this module.

Namespace Clashes¶

It is possible to have a namespace clash in Java, despite the packaging system!

Consider the example below:

package io.entityfour;

import java.util.Date;
import java.sql.Date;

public class DatePrinter {
 public void printDate(Date aDate){
  System.out.println(aDate.toString());
 }
 public void printSQLDate(Date aDate){
  System.out.println(aDate.toString());
 }
}

Both java.util.Date and java.sql.Date have been imported. This causes a name collision within the imported classes.

This can be resolved by using the fully qualified class name for one or both of the classes.

package io.entityfour;

import java.util.Date;

public class DatePrinter {
 public void printDate(Date aDate){
  System.out.println(aDate.toString());
 }
 public void printSQLDate(java.sql.Date aDate){
  System.out.println(aDate.toString());
 }
}

Implicit Imports¶

All Java class file implicitly include the following import statement: import java.lang.*;

java.lang is a package that supports a set of classes that provide essential Java language and runtime services. This includes:

• String - A class for manipulating immutable character strings
• StringBuilder - A class for dynamically building mutable character strings
• System - A class for interfacing with the operating system