Java

INDEPENDENT TOPIC 06 – CHARACTERS

LESSON NOTE

INTRO

One type of variable that is used less often but is useful at times is the char variable. It holds a simple character.

The variable type char, which is short for character, can be pronounced in many ways including kar, care, character and tchar. We will mostly use tchar in class.

CHAR LITERALS

Just like String literals are placed inside double quotes, a character literal is places inside single quotes.

VARIABLE DECLARATION AND INITIALIZATION

We can declare a char variable named letter by using:

char letter;

We can declare and initialize a char variable named let to the character b by using:

char let = 'b';

INTEGER VALUE

Each char is associated with an integer value.

We can get the int value of a char by simply type casting it into an int variable.

char c = 'a';

System.out.println(c); //a

int i = (int)c;

System.out.println(i); //97

ASCII CHART

The ascii chart gives a listing of characters and their integer value.

Click here to see the ascii chart. Note that the integer value is listed as “Decimal” on the chart.

Notice that ‘a’ is 97 and ‘b’ is 98 and ‘c’ is 99 and so on… Also notice that there are different integer values for ‘A’, ‘B’ and ‘C’. There are also numbers for different characters including numbers.

SHIFTING CHARACTERS

Given a character, we can output the next character in the ascii chart by type casting that char into an int, then adding 1, then type casting it back into a char. This is called shifting.

char c = 'a';

System.out.println(c); //a

int i = (int)c;

System.out.println(i); //97

int j = i + 1;

System.out.println(j); //98

char c2 = (char)j;

System.out.println(c2); //b

A shorter version of the above code would be:

char c = 'a';

System.out.println(c); //a

char c2 = (char)((int)c + 1);

System.out.println(c2); //b

Notice that the ascii chart has two full alphabets. The difference between the int value of capital letters and lower case letters is 32. If that is unclear, see that ‘A’ is 65 and ‘a’ is 97 and the difference of the two is 32. The same value applies for any other letter.

So, we can shift a char from upper case to its lower case version by adding 32.

char c = 'T';

int i = (int)c + 32;

char c2 = (char)i;

System.out.println(c2); //t

And of course, we could go from lower case to upper case by subtracting 32 instead.

CHARS IN IF STATEMENTS

We can use char variables in if statements like all other variables. In fact, you can use all of the common operators: ==, !=, <, <=, > and >=.

char ch1 = 'A'; //int value of 65

char ch2 = 'B'; //int value of 66

System.out.println(ch1 == ch2); //false

System.out.println(ch1 != ch2); //true

System.out.println(ch1 < ch2); //true

System.out.println(ch1 <= ch2); //true

System.out.println(ch1 > ch2); //false

System.out.println(ch1 >= ch2); //false

We can therefore check which letter comes first in the alphabet.

char ch1 = 'T'; //int value of 84

char ch2 = 'D'; //int value of 68

if (ch1 < ch2)

{

System.out.println(ch1 + " comes first.");

}

else

{

System.out.println(ch2 + " comes first.");

}

The program above outputs: “D comes first”.

Warning: The above code only works if both characters are of the same case. If one is upper case and the other is lower case, then the upper case char will always have a smaller int value.

GETTING A CHAR FROM A STRING

All characters in a String are numbered. The first is numbered 0, then the next is number 1 and so on. We can use the charAt method inside the String class to get a char that is at a specific position in the String.

String s = "Campeau";

char ch1 = s.charAt(2);

System.out.println(ch1); //m

The code above will output 2, because the char m is in position 2 inside the String.

THE CHARACTER CLASS

Java has a built-in Character class that provides some useful functions when working with char variables. We will explore a few below:

CHECKING THE CASE

One way to check if a character was a lower case char would be to see if its int value was between 97 and 122 inclusively. However, there is a built-in option as well.

We can use Character.isUpperCase(char) to see if char is upper case or not.

char ch = 'G';

if (Character.isUpperCase(ch))

{

System.out.println("Upper Case!");

}

else

{

System.out.println("Lower Case!");

}

Of course, there is also Character.LowerCase(char) that returns true if char is in lower case.

CHECKING FOR A LETTER

We can check if a char is a letter by using Character.isLetter(char).

char ch = '7';

if (Character.isLetter(ch))

{

System.out.println("Letter!");

}

else

{

System.out.println("Not letter!");

}

CHECKING FOR A NUMBER (DIGIT)

We can check if a char is a digit by using Character.isDigit(char).

char ch = '2';

if (Character.isDigit(ch))

{

System.out.println("Digit!");

}

else

{

System.out.println("Not digit!");

}