Java 判断字符是否为数字

String str = "123abc";

for(int i =0, length = str.length(); i<length;i++)

{

System.out.println("char: "+str.charAt(i));

System.out.println("ASCII: "+(int)str.charAt(i));

if (Character.isDigit(str.charAt(i)))

System.out.println("Character.isDigit(str.charAt(0)) - yes");

else

System.out.println("Character.isDigit(str.charAt(0)) - no");

if(str.charAt(i) > 48 && str.charAt(i) <57)

System.out.println("str.charAt(0) > 48 && str.charAt(0) <57 - yes");

else

System.out.println("str.charAt(0) > 48 && str.charAt(0) <57 - no");

if((int)str.charAt(i) > 48 && (int)str.charAt(i) <57)

System.out.println("(int)str.charAt(0) > 48 && (int)str.charAt(0) <57 - yes");

else

System.out.println("(int)str.charAt(0) > 48 && (int)str.charAt(0) <57 - no");

if(str.charAt(i) <= '9' && str.charAt(i) >= '0')

System.out.println("str.charAt(0) <= '9' && str.charAt(0) >= '0' - yes");

else

System.out.println("str.charAt(0) <= '9' && str.charAt(0) >= '0' - no");

}

输出结果：

char: 1

ASCII: 49

Character.isDigit(str.charAt(0)) - yes

str.charAt(0) > 48 && str.charAt(0) <57 - yes

(int)str.charAt(0) > 48 && (int)str.charAt(0) <57 - yes

str.charAt(0) <= '9' && str.charAt(0) >= '0' - yes

char: 2

ASCII: 50

Character.isDigit(str.charAt(0)) - yes

str.charAt(0) > 48 && str.charAt(0) <57 - yes

(int)str.charAt(0) > 48 && (int)str.charAt(0) <57 - yes

str.charAt(0) <= '9' && str.charAt(0) >= '0' - yes

char: 3

ASCII: 51

Character.isDigit(str.charAt(0)) - yes

str.charAt(0) > 48 && str.charAt(0) <57 - yes

(int)str.charAt(0) > 48 && (int)str.charAt(0) <57 - yes

str.charAt(0) <= '9' && str.charAt(0) >= '0' - yes

char: a

ASCII: 97

Character.isDigit(str.charAt(0)) - no

str.charAt(0) > 48 && str.charAt(0) <57 - no

(int)str.charAt(0) > 48 && (int)str.charAt(0) <57 - no

str.charAt(0) <= '9' && str.charAt(0) >= '0' - no

char: b

ASCII: 98

Character.isDigit(str.charAt(0)) - no

str.charAt(0) > 48 && str.charAt(0) <57 - no

(int)str.charAt(0) > 48 && (int)str.charAt(0) <57 - no

str.charAt(0) <= '9' && str.charAt(0) >= '0' - no

char: c

ASCII: 99

Character.isDigit(str.charAt(0)) - no

str.charAt(0) > 48 && str.charAt(0) <57 - no

(int)str.charAt(0) > 48 && (int)str.charAt(0) <57 - no

str.charAt(0) <= '9' && str.charAt(0) >= '0' - no