• Go more in depth about characters and ASCII values
• Discuss escape sequences
• Explain character arrays and strings

So far, we have seen the char data type reference in passing, and we know it stores a single character or ASCII value, but we really haven't used it or talked too in-depth about it. In this section, we will explore characters some more, talk about what an ASCII value is, point out a few special characters, and explain how it might relate to the String class.

A char is a primitive data type that takes up to 2 bytes of memory. We may recall from the Variables' lesson that a char stores a single character or an ASCII value.

char grade = 'A';

The above code is how we would initialize a char data type. A char variable can be assigned a value by enclosing the character in single quotes, such as 'A'.

The char data type can also be considered a numeric value. If we remember from the Type Casting lesson, we said that a char could be upcasted to an int, long, float, or double. This means, in Java, it treats char as a number. We might be wondering, "But how?" since 'A' is clearly a letter and not a number. But all characters can actually be converted to a decimal number! This brings us to what an ASCII table is:

Medium: ASCII Table in Java Programming

An ASCII Table is a tabular representation that links characters to decimal values. We can see what each letter represents using this ASCII table. We can also see that the uppercase characters have different values from the lowercase letters. This means that 'A' would not be the same as 'a' in Java!

Let's consider our example again: char grade = 'A'; We can see in the ASCII table that the character 'A' has a decimal value of 65. Does this mean, that if we set char grade to the number 65 that it would be the same as setting it to 'A'?

char firstGrade = 'A';
char secondGrade = 65;
if (firstGrade == secondGrade) {
    System.out.println("Wow! 'A' is the same as 65!");
} else {
    System.out.println("Told you 'A' wasn't the same as 65!");
}

The output to the code above is:

Wow! 'A' is the same as 65!

As we can now see, the definition of a char data type makes more sense when we say "stores a single character or an ASCII value" since we could set it to either a numeric value or use single quotes to wrap a character! For readability in Java, we tend to set char data types to the characters using single quotes instead of using the decimal values. In other words, char grade = 'A'; is preferred over char grade = 65;.

Java also has several special characters. These special characters can be accessed using the backslash character '', also known as the escape character. Whatever follows the escape character is known as an escape sequence.

For example, if we want to use a double quotation mark within a String, we can use the escape sequence \". The backslash escapes the double quote and in turn, tells Java that we are to use the double quote within the String and not end the String (since we usually wrap String values in double quotes). Let's look at an example of this:

System.out.println("\"You must be the change you wish to see in the world.\" - Mahatma Gandhi");

Output:

"You must be the change you wish to see in the world." - Mahatma Gandhi

Notice how the backslashes are not printed but the double quote immediately following the backslash is printed. This is because the escape character notifies Java that we are to print the escape sequence instead that results in just a double quotation mark. Java also treats the escape sequence as one character - meaning \" would be considered one character, not two.

Consider the table of escape sequences:

A few notes on the escape sequences: The tab and new line characters are representatives of whitespace. Consider the example below of how to use these characters:

String firstString = "Hello\tWorld!";
String secondString = "What a beautiful\nday!";

System.out.println(firstString);
System.out.println(secondString);

Output:

Hello   World!
What a beautiful
day!

We can see in the above output that when we placed the character \t between "Hello" and "World!", it placed a tab or an indent between the two words. In the secondString, we place a \n character between the words "beautiful" and "day!". When we print that to the screen, it will actually write the word "day!" on a new line separate from "What a beautiful".

A sequence of characters can be treated as a single unit... and that is where the String data type comes in. But we also just learned about arrays. So wouldn't an array of characters be the same thing as a String?

The answer is: no - but pretty close!

In Java, there are a few differences between a String and a char[]:

1. A String is a sequence of characters where a char[] is a collection of char data types. In a char[], each element could be treated independently and separately. For example, we could have a character array of grades: char[] grades = {'A', 'B', 'C', 'D', 'F'};.
2. A String is an immutable type whereas a char[] is still mutable.
3. We can use a + to concatenate two String values together but cannot do the same for a character array.
4. The String class has built-in methods that we will cover in the next couple of lessons. But a char[] does not have any built-in methods; however, we can pass it in as a parameter to the Arrays class as we saw with the method Arrays.sort().

There is a way for us to convert a character array into a String though and vice versa!

To convert a character array into a String, we could make use of the String constructor:

char[] gradesAsCharArray = {'A', 'B', 'C', 'D', 'F'};
String gradesAsString = new String(gradesAsCharArray);

To convert a String into a character array, we can actually use a method of the String class called toCharArray(). We will learn more about the methods within the String class in the next lesson, but here is how we can use that method to go from a String to a char[].

String gradesAsString = "ABCDF";
char[] gradesAsCharArray = gradesAsString.toCharArray();

• Medium: ASCII Table in Java Programming