Quickref - ArrayBuffer, HashMap, and HashSet for gaming

Note – An Arraybuffer is a type of sequence (containing a sequence of elements one after the other). In other languages, ArrayBuffers are variously known as Lists, Arrays, Vectors, ArrayLists, etc.

• 1 ArrayBuffer
• 1.1 Creation
• 1.2 Addition of elements at the end
• 1.3 Iteration over all the elements
• 2 HashMap
• 2.1 Creation
• 2.2 Addition of key, value pairs
• 2.3 Lookup of values based on keys
• 3 HashSet
• 3.1 Creation
• 3.2 Addition of objects
• 3.3 Iteration over all the elements
• 3.4 Removal of objects
• 3.5 Containment check

1 ArrayBuffer

An ArrayBuffer is a sequence of elements. Every element can be located based on its position or index within the ArrayBuffer.

Positions (or indices) start from 0 and go upto length - 1.

Here is a pictorial representation of an ArrayBuffer:

The following are the primary operations that you can do with an ArrayBuffer:

1.1 Creation

• ArrayBuffer.empty[type] - creates an empty ArrayBuffer which will hold elements of the given type.

Example:

ArrayBuffer.empty[Int]
ArrayBuffer.empty[Picture]

• ArrayBuffer(e1, e2, e3) - creates an ArrayBuffer with the given elements

Example:

ArrayBuffer(4, 9, 7)
ArrayBuffer(pic1, pic2, pic3, pic4)

1.2 Addition of elements at the end

• ab.append(element) - adds element to the end of an ArrayBuffer called ab.

Assume that you have created an ArrayBuffer of Ints called ab1 and and ArrayBuffer of Pictures called ab2, and that you have a Picture called pic5.

Example:

ab1.append(7)
ab2.append(pic5)

1.3 Iteration over all the elements

Iterating over the elements means going over all the elements (to do something with each)

• repeatFor(ab) { e => /* do whatever with e /* } - iterators over all the elements of an ArrayBuffer called ab. While iterating, the current element is called e in the given example. Your code can do whatever it wants with e.

Assume that you have created an ArrayBuffer of Ints called ab1 and an ArrayBuffer of Pictures called ab2.

Example:

repeatFor(ab1) { n =>
    println(n)
}

repeatFor(ab2) { p =>
    draw(p)
}

2 HashMap

Note – A HashMap is a type of Map (mapping a key to a value). In other languages, HashMaps are variously known as Maps, Dictionaries, etc.

A HashMap is a collection of key-value pairs. You can add key-value pairs to a HashMap, and quickly look up the values for given keys.

Here is a pictorial representation of a HashMap:

The following is a description of the primary operations that you can do with a HashMap:

2.1 Creation

• HashMap.empty[type1, type2] - creates an empty HashMap which will hold keys of type1 and values of type2.

Example:

HashMap.empty[String, Int]
HashMap.empty[Picture, Vector2D]

2.2 Addition of key, value pairs

• hm(key) = value - adds the pair (key, value) to a HashMap called hm.

Assume that you have created a HashMap of String to Int called hm1 and a HashMap of Pictures to Vector2Ds called hm2, and that you have Pictures called pic1 and pic2.

Example:

hm1("Aditya") = 12
hm1("Ushi") = 12

hm2(pic1) = Vector2D(1, 1)
hm2(pic2) = Vector2D(12, 13)

2.3 Lookup of values based on keys

• hm(key) - gives you the value that corresponds to the given key in a HashMap called hm.

Assume that you have created a HashMap of String to Int called hm1 and a HashMap of Pictures to Vector2Ds called hm2, and that you have Pictures called pic1 and pic2.

Example:

println(hm1("Aditya"))
println(hm1("Ushi"))

pic1.translate(hm2(pic1))
pic2.translate(hm2(pic2))

3 HashSet

Note – A HashSet is a type of Set (an unordered collection of values).

A HashSet is an unordered collection of objects. Checking if an object is present in a set, or removing an object from a set - is very efficient.

Here is a pictorial representation of a HashSet:

The following is a description of the primary operations that you can do with a HashSet:

3.1 Creation

• HashSet.empty[type] - creates an empty HashSet which will hold elements of the given type.

Example:

HashSet.empty[String]
HashSet.empty[Picture]

3.2 Addition of elements

• hs.add(value) - adds value to a HashSet called hs.

Assume that you have created a HashSet of String called hs1 and a HashSet of Picture called hs2, and that you have Pictures called pic1 and pic2.

Example:

hs1.add("Aditya")
hs1.add("Ushi")

hs2.add(pic1)
hs2.add(pic2)

3.3 Iteration over all the elements

As mentioned earlier, iterating over the elements means going over all the elements (to do something with each)

• repeatFor(hs) { e => /* do whatever with e /* } - iterators over all the elements of a HashSet called hs. While iterating, the current element is called e in the given example. Your code can do whatever it wants with e.

Assume that you have created a HashSet of Strings called hs1 and a HashSet of Pictures called hs2.

Example:

repeatFor(hs1) { n =>
    println(n)
}

repeatFor(hs2) { p =>
    draw(p)
}

3.4 Removal of objects

• hs.remove(value) - removes value from hs.

Assume that you have created a HashSet of String called hs1 and a HashSet of Picture called hs2, and that you have Pictures called pic1 and pic2 that you have already put inside hs2.

Example:

hs1.remove("Aditya"))

hs2.remove(pic1)
hs2.remove(pic2)

3.5 Containment check

• hs(value) or hs.contains(value) - tells you whether value is present in hs.

Assume that you have created a HashSet of String called hs1 and a HashSet of Picture called hs2, and that you have Pictures called pic1 and pic2.

Example:

println(hs1("Aditya"))
println(hs1.contains("Ushi"))

println(hs2(pic1))
println(hs2.contains(pic2))