Return to main page
View source or report issues on GitHub

Common Data Types

In previous notes, we mentioned that the bits and bytes on a computer can be interpreted in lots of different ways.

One of the ways our computer programs know how to interpret a byte (or more) of data in the context of a programming language is by the type of the data, which is set in the program. Every variable in a program can hold data of a specific type.

In a program, there are three types of things that have types:

Variables are named locations in memory whose value may change over the course of the program.
Constants are like variables but their value will always be the same
Literals are individual elements like 2 or "abc" that are used only once and represent a value directly.

General Type	Languague-specific usage	Description
Boolean	TypeScript `let boo:boolean=true;` java `boolean boo=false;`	The value of a boolean is either `true` or `false`. The simplest data type!
Numeric	TypeScript `let n:number=1;` `let x:number=3.21;` java `int n=11;` `double x=1.2;`	Holds a number. In TypeScript and javascript, all numbers are floating point numbers (meaning they can be integers or decimals) while java separates decimals (called doubles for historical reasons) from integers. There are advantages to both systems.
Characters and Strings	Typescript `let k:string="word";` java `char c='a';` `String s="12";`	A character is a single piece of text data, ready to print to the screen, such as the character `'a'` or `'8'` or `'â'` or even `'😀'`. If you combine more than one character, you get a string, like `"string83"`. In javascript / TypeScript, characters are just small strings, but in java they are separate types of data with different rules. Strings and characters are always surrounded by quotation marks.
Arrays	TypeScript `let a:number[]=[1, 2, 3];` java `boolean[] a={true, false};`	A collection of more than one item of any type (even other arrays!). `type[]` in either language creates a group that can hold many values of the given type.
Objects	Much more later!	A group of many related values and functions that work together as one larger thing. The center of object-oriented programming. Objects often have their own special names.

Check your Understanding

What type of data is the value 234 in TypeScript? What is it in java?

Click to expand answer

Typescript: number java: int
You want to write the code j = "bob". What data type must j be declared as for this to not give an error?
Click to expand answer
```
1
string
```
The following TypeScript code gives an error. Why?
```
1
2
let j:string;
j = 123;
```
Click to expand answer

j is a string but you are trying to assign it a number
The following java code gives an error. Why?
```
1
2
 int j;
 j = "123";
```
Click to expand answer

j is an integer, but you are assigning it a string.
You write the following code:
```
1
let b = (2 + 2 > 4);
```
What do you think is the VALUE and TYPE of b? (cool thing to try: you can check your answer by typing “ts-node” on your command line, then typing that code. After pressing enter, type b to output its value. Type .exit (notice the period!) to exit.)

Click to expand answer

b is a boolean, with the value false

Study Materials

Bitmoji Books Create flash cards or a quizlet deck with the following words, with examples, a description, and a code example for TypeScript and java on the back.

Boolean
Number
Integer
Floating Point Number (double)
Character
String
Array
Object

We have a quizlet class at https://quizlet.com/join/S8XGx3k93 and you can add your decks there if you make them, but you REALLY should make your own deck before using those of others. You learn as much from making the flashcards as using them, if not more.