Java Character class

May 10, 2021 Java

Java Character class

When using characters, we typically use built-in data type char.

Instance

char ch = 'a';

// Unicode for uppercase Greek omega character
char uniChar = '\u039A'; 

// 字符数组
char[] charArray = { 'a', 'b', 'c', 'd', 'e' };

However, in the actual development process, we often encounter situations where we need to use objects rather than built-in data types. To solve this problem, the Java language provides a wrapper character class for the built-in data type char.

The Character class provides a series of ways to manipulate characters. You can use Character's construction methods to create a Character class object, for example:

Character ch = new Character('a');

In some cases, the Java compiler automatically creates a Character object.

For example, when you pass an argument of a char type to a Character type parameter that is required, the compiler automatically converts the char type parameter to a Character object. T his feature is called boxing, which in turn is called unboxing.

Instance

// Here following primitive char 'a'
// is boxed into the Character object ch
Character ch = 'a';

// Here primitive 'x' is boxed for method test,
// return is unboxed to char 'c'
char c = test('x');

Escape sequence

Characters with backslashes in front of them represent escape characters, which have a special meaning for the compiler.

The following list shows the escape sequence for Java:

Escape sequence	Describe
\t	Insert a tab key there
\b	Insert a back key there
\n	Line up there in the text
\r	Insert a carriage return at this place in the text
\f	Insert a page break there
\'	Insert single quotes there
\"	Insert double quotes there
\\	Insert a backslash there

Instance

When a print statement encounters an escape sequence, the compiler interprets it correctly.

public class Test {

   public static void main(String args[]) {
      System.out.println("She said \"Hello!\" to me.");
   }
}

The above examples compile and run as follows:

She said "Hello!" to me.

Character method

Here's how the Character class is:

Serial number	Method and description
1	isLetter() Whether it is a letter
2	isDigit() Whether it is a numeric character
3	isWhitespace() Whether it's a space
4	isUpperCase() Whether it's capital letters or not
5	isLowerCase() Whether it's a lowercase letter
6	toUpperCase() Specifies the capital form of the letter
7	toLowerCase() Specify the lowercase form of the letter
8	toString() Returns the string form of the character, which is only 1 in length

Beginners often use several methods

public static boolean isUpperCase (char ch): to determine whether a given character is capital character;
public static boolean is LowerCase (char ch): to determine whether a given character is a small-case character;
public static boolean is Digit (char ch): to determine whether a given character is a numeric character;
The boolean representation in these three sentences, the return value of the three methods used, is the boolean type.

Instance

public class Java {

	public static void main(String[] args) {
		Character ch = new Character('X');
		
		System.out.println(Character.isUpperCase(ch));
		//Character.isUpperCase(ch) 用于判断括号里的字母是否为大写
		System.out.println(Character.isLowerCase(ch));
		//Character.isLowerCase(ch) 用于判断括号里的字母是否为小写
		System.out.println(Character.isDigit(ch));
		//Character.isDigit(ch) 用于判断括号里的内容是否为数字
	}
}

The results are:

true
false
false

For a complete list of methods, refer to the java.lang.Character API specification.

Java Character class

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