Java Character 类
Character 包装类的创建、转义序列与常用判断转换方法。
Key PointsCharacter 是 char 的包装类，提供 isLetter/isDigit/isWhitespace 等判断和 toUpperCase/toLowerCase 转换。
Character 的创建
Character wraps a single char; assign directly for autoboxing. It implements Comparable, so characters compare naturally.
Java
public class CharCreate {
public static void main(String[] args) {
Character c1 = 'A';
char c2 = 'b';
System.out.println(c1);
System.out.println(c2);
System.out.println(c1.compareTo('C'));
System.out.println((int) c1);
}
}Output
A
b
-2
65转义序列
Java escapes start with a backslash: \n newline, \t tab, \r carriage return, \\ backslash, \' quote, \" double quote and \uXXXX for a Unicode code point.
Java
public class Escape {
public static void main(String[] args) {
System.out.print("a\tb\n");
System.out.print("quote: \' and \"\n");
System.out.print("backslash: \\\n");
System.out.print("\u4E2D\u6587\n");
}
}Output
a b
quote: ' and "
backslash: \
中文Character 方法
Predicates: isLetter, isDigit, isWhitespace, isUpperCase, isLowerCase. Converters: toUpperCase, toLowerCase, toString. All are static.
| Method | Returns |
|---|---|
| isLetter(ch) | true if a letter |
| isDigit(ch) | true if 0-9 |
| isWhitespace(ch) | true for space/tab/newline |
| isUpperCase(ch) | true if uppercase |
| toUpperCase(ch) | converted char |
| toLowerCase(ch) | converted char |
Java
public class CharMethods {
public static void main(String[] args) {
char c = 'A';
System.out.println(Character.isLetter(c));
System.out.println(Character.isDigit('7'));
System.out.println(Character.isWhitespace(' '));
System.out.println(Character.isUpperCase(c));
System.out.println(Character.toLowerCase(c));
System.out.println(Character.toUpperCase('b'));
}
}Output
true
true
true
true
a
BCharacter 的创建
Character 包装一个 char 值，可以直接赋值（自动装箱）或用构造方式。它继承了 Comparable，所以能直接比较大小。
Java
public class CharCreate {
public static void main(String[] args) {
Character c1 = 'A';
char c2 = 'b';
System.out.println(c1);
System.out.println(c2);
System.out.println(c1.compareTo('C'));
System.out.println((int) c1);
}
}Output
A
b
-2
65转义序列
Java 的转义序列用反斜杠开头：\n 换行、\t 制表、\r 回车、\\ 反斜杠、\' 单引号、\" 双引号、\uXXXX Unicode 码位。
Java
public class Escape {
public static void main(String[] args) {
System.out.print("a\tb\n");
System.out.print("quote: \' and \"\n");
System.out.print("backslash: \\\n");
System.out.print("\u4E2D\u6587\n");
}
}Output
a b
quote: ' and "
backslash: \
中文Character 方法
常用判断方法：isLetter、isDigit、isWhitespace、isUpperCase、isLowerCase；转换方法：toUpperCase、toLowerCase、toString。都是静态方法。
| 方法 | 返回 |
|---|---|
| isLetter(ch) | 是否为字母 |
| isDigit(ch) | 是否为数字字符 |
| isWhitespace(ch) | 是否为空白字符 |
| isUpperCase(ch) | 是否为大写 |
| toUpperCase(ch) | 转为大写 |
| toLowerCase(ch) | 转为小写 |
Java
public class CharMethods {
public static void main(String[] args) {
char c = 'A';
System.out.println(Character.isLetter(c));
System.out.println(Character.isDigit('7'));
System.out.println(Character.isWhitespace(' '));
System.out.println(Character.isUpperCase(c));
System.out.println(Character.toLowerCase(c));
System.out.println(Character.toUpperCase('b'));
}
}Output
true
true
true
true
a
B