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► KB ► To/From Guides ► Java ► Data Structures

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Cross Ref > Data Structures

By Mike Prestwood

Java versus C#: A side by side comparison between Java and C#.

Data Structures

Data structures allow you to store and work with data. Common data structures include arrays, associative arrays, etc.

Associative Array

[Other Languages]

A set of unique keys linked to a set of values. Each unique key is associated with a value. Think of it as a two column table. MyArray['CA'] = 'California' MyArray['AR'] = 'Arizona'

Languages Focus

Associative arrays are also known as a dictionary or a hash table in other languages.

Java: HashMap()

An associative array links a set of keys to a set of values. In Java, associative arrays are implemented as Maps.

This will print "Arizona."

Syntax Example:

import java.util.*;

public class Maps 
{
    public static void main(String[] args) 
    {
        Map states = new HashMap();
        
        states.put("CA", "California");
        states.put("FL", "Florida");
        states.put("AZ", "Arizona");

        System.out.println(states.get("AZ"));
    }
}

Associative Arrays in Java (a Map)

C#: Dictionary

Syntax Example:

//using System.Collections.Generic;

Dictionary <String, String> airports = new Dictionary <String, String>();

airports.Add("LAX", "Los Angeles"); 
airports.Add("SFO", "San Francisco"); 
airports.Add("SAN", "San Diego");

MessageBox.Show(airports["LAX"]);

C# Associative Array (Dictionary)

Pointers

[Other Languages]

General Info: Pointers / References

A pointer is a variable type that allows you to refer indirectly to another object. Instead of holding data, a pointer holds the address to data -- the address of another variable or object. You can change the address value a pointer points to thus changing the variable or object the pointer is pointing to.

A reference is a type of pointer that cannot change and it must always point to a valid storage (no nulls).

Java: Not Supported

Java does not offer developer defined pointers.

C#:

Although pointer data types in C# coding are less important than in other languages such as C++, C# does support developer defined pointers. Use the * operator to declare a pointer data type. Use the & operator to return the current address of a variable.

In .Net managed coding the use of pointers is not safe because the garbage collector may move memory around. To safely use pointers, use the unsafe keyword. However, avoid unsafe code if possible.

C++/CLI has more extensive support for pointers than C#. If you have needs that go beyond what C# offers, you can code in C++/CLI and add it to your project.

Syntax Example:

//Declare a pointer of type integer.

Integer *PCounter;