Class Diagram

The class diagram is a static diagram which describes the class structure of an application.

It is the most common starting point for software developers and architects when designing a system.

Class

A class is represented with a box containing three parts.

• Name
• Attributes (fields)
• Methods

Visibility

We denote the visibility of attributes and methods with the following notations.

Marker	Visibility
+	public
#	protected
~	package
-	private

Attributes (Fields)

Attributes are listed by name:Type.

We add a visibility notation before each field.

static fields are underlined.

For the fields

  private String str;
  protected int intField;

...we write

- str: String
# intField: int

Methods

Each method is written using its signature and return type, in the form visibility signature():ReturnType.

Constructors do not list a return type.

For the constructor and methods

  public ExampleClass(){

  }

  public String getStr() {
    return str;
  }

  public void setStr(String str) {
    if(str == null) {
      str = "";
    }
    this.str = capitalizeStr(str);
  }

  private String capitalizeStr(String input) {
    return input.toUpperCase();
  }

...we write

+ ExampleClass()
+ getStr():String
+ setStr(String):void
- capitalizeStr(String):String

Note that we do not use parameter names in the parentheses, just their types.

Example Diagram

Note the private and protected fields, and public and private methods, of this class:

public class ExampleClass {
  private String str;
  protected int intField;

  public ExampleClass() {

  }

  public String getStr() {
    return str;
  }

  public void setStr(String str) {
    if(str == null) {
      str = "";
    }
    this.str = capitalizeStr(str);
  }

  private String capitalizeStr(String input) {
    return input.toUpperCase();
  }
}

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