{"id":1475,"date":"2018-10-30T13:54:48","date_gmt":"2018-10-30T13:54:48","guid":{"rendered":"https:\/\/www.courses.tegabrain.com\/cc18\/?page_id=1475"},"modified":"2018-10-30T16:39:36","modified_gmt":"2018-10-30T16:39:36","slug":"inheritance-and-polymorphism-in-p5js","status":"publish","type":"page","link":"https:\/\/www.courses.tegabrain.com\/cc18\/inheritance-and-polymorphism-in-p5js\/","title":{"rendered":"Inheritance and polymorphism in p5JS"},"content":{"rendered":"

You may have encountered the terms inheritance<\/em> and polymorphism<\/em> in your programming life before this book. After all, they are two of the three fundamental principles behind the theory of object-oriented programming (the other being encapsulation<\/em>). This is covered in other Processing or Java programming books too. The text, Learning Processing<\/em>, has close to an entire chapter (#22) dedicated to these two topics.<\/p>\n

Inheritance basics.<\/h3>\n

Let\u2019s take a different example, the world of animals: dogs, cats, monkeys, pandas, wombats, and sea nettles. We\u2019ll start by programming a Dog<\/span> class. A Dog<\/span> object will have an age variable (an integer), as well as eat()<\/span>, sleep()<\/span>, and bark()<\/span> functions.<\/p>\n

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class<\/span> Dog<\/span> {<\/span><\/span>\r\n\r\n   contructor<\/span>() {  \r\n    this.age<\/span> = 0<\/span>;  \r\n   } \r\n \r\n   eat<\/span>() {  \r\n    println<\/span>(\"Yum!\"<\/span>);  \r\n   }  \r\n\r\n   sleep<\/span>() {  \r\n   println<\/span>(\"Zzzzzz\"<\/span>);  \r\n   }\r\n\r\n   bark<\/span>() {  \r\n    println<\/span>(\"WOOF!\"<\/span>);  \r\n   }\r\n  }\r\n\r\n<\/span><\/span><\/pre>\n<\/div>\n
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Dogs and cats have the same variables (age) and functions (eat, sleep).<\/div>\n<\/div>\n
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A unique function for barking.<\/div>\n<\/div>\n<\/div>\n<\/div>\n
Now, let\u2019s move on to cats.<\/p>\n
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class<\/span> Cat<\/span> {\r\n<\/span><\/span>\r\n  constructor<\/span>()<\/span> {<\/span><\/span>\r\n    this.age<\/span> =<\/span> 0<\/span>;<\/span><\/span>\r\n  }<\/span><\/span>\r\n \r\n  eat<\/span>()<\/span> {<\/span><\/span>\r\n    println<\/span>(<\/span>\"Yum!\"<\/span>);<\/span><\/span>\r\n  }<\/span><\/span>\r\n \r\n  sleep<\/span>()<\/span> {<\/span><\/span>\r\n    println<\/span>(<\/span>\"Zzzzzz\"<\/span>);<\/span><\/span>\r\n  }<\/span><\/span>\r\n \r\n  meow<\/span>()<\/span> {<\/span><\/span>\r\n    println<\/span>(<\/span>\"MEOW!\"<\/span>);<\/span><\/span>\r\n  }<\/span><\/span>\r\n}<\/span><\/span><\/pre>\n<\/div>\n<\/div>\n
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As we rewrite the same code for fish, horses, koalas, and lemurs, this process will become rather tedious. Instead, let\u2019s develop a generic Animal<\/span> class that can describe any type of animal. All animals eat and sleep, after all. We could then say:<\/p>\n
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  • A dog is an animal and has all the properties of animals and can do all the things animals do. Also, a dog can bark.<\/li>\n
  • A cat is an animal and has all the properties of animals and can do all the things animals do. Also, a cat can meow.<\/li>\n<\/ul>\n<\/div>\n
    Inheritance makes this all possible. With inheritance, classes can inherit properties (variables) and functionality (methods) from other classes. A Dog<\/span> class is a child (subclass<\/em><\/strong>) of an Animal<\/span> class. Children will automatically inherit all variables and functions from the parent (superclass<\/em><\/strong>), but can also include functions and variables not found in the parent. Like a phylogenetic “tree of life,” inheritance follows a tree structure. Dogs inherit from canines, which inherit from mammals, which inherit from animals, etc.<\/p>\n
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    \"Nature<\/p>\n
    Figure 4.2<\/p>\n<\/div>\n
    Here is how the syntax works with inheritance.<\/p>\n
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    The Animal class is the parent (or super) class.<\/div>\n
    \/\/animal class is the parent class\r\n\r\nclass Animal { \r\n\r\n\/\/Dog and Cat inherit the variable age.\r\n\r\n  constructor() {\r\n    this.age = 0; \r\n  }\r\n\r\n\/\/Dog and Cat inherit the functions eat() and sleep().\r\n\r\n  eat() {\r\n    println(\"Yum!\");\r\n  }\r\n \r\n  sleep() {\r\n    println(\"Zzzzzz\");\r\n  }\r\n}\r\n \r\n\r\n\/\/The Dog class is the child (or sub) class, indicated by the code \"extends Animal\".\r\n\r\nclass Dog extends Animal {\r\n  constructor() {\r\n    super(); \/\/super() executes code found in the parent class.\r\n  }\r\n\r\n\/\/We define bark() in the child class, since it isn't part of the parent class.\r\n  bark() {\r\n    println(\"WOOF!\");\r\n  }\r\n}\r\n \r\nclass Cat extends Animal {\r\n  constructor() {\r\n    super();\r\n  }\r\n\r\n  meow() {\r\n    println(\"MEOW!\");\r\n  }\r\n}\r\n<\/pre>\n
    This brings up two new terms:<\/div>\n<\/div>\n<\/div>\n<\/div>\n
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