如果用户输入十进制，分数，混合分数或无效，我如何确定用户的输入？
这是我程序中允许的输入
String[] s = new String[]{ "0",".",".0",".01","1.","1.0","1.01", "1 ","1 1","1/2","1/","1/0", "1 1/1", "1 0/0","1 /","1 /0", "1 0/"};
预期产出：
0) 0 ---- Zero
1) . ---- Error
2) .0 ---- Zero
3) 0.01 ---- Decimal
4) 1. ---- Decimal(the input 1. should be turned to decimal)
5) 1.0 ---- Decimal
6) 1.01 ---- Decimal
7) 1 ---- Decimal(the input with space after the whole number must be decimal)
8) 1 1 ---- Error(because of the space between the 1)
9) 1/2 ---- Fraction
10) 1/ ---- Error
11) 1/0 ---- Error
12) 1 1/1 ---- Mixed Fraction
13) 1 0/0 ---- Error
14) 1 / ---- Error
15) 1 /0 ---- Error
16) 1 0/ ---- Error
实际输出：
0) 0 ---- Zero
1) . ---- Error
2) .0 ---- Zero
3) 0.01 ---- Decimal
4) 1. ---- Error
5) 1.0 ---- Decimal
6) 1.01 ---- Decimal
7) 1 ---- Error
8) 1 1 ---- Mixed Fraction
9) 1/2 ---- Fraction
10) 1/ ---- Fraction
11) 1/0 ---- Fraction
12) 1 1/1 ---- Mixed Fraction
13) 1 0/0 ---- Error
14) 1 / ---- Error
15) 1 /0 ---- Error
16) 1 0/ ---- Error
我对如何建立良好的正则表达式模式知之甚少？
我的代码：
public class DecimalOrFraction {
public static void main(String args[]){
String[] s = new String[]{ "0",".",".0",".01","1.","1.0","1.01", "1 ","1 1","1/2","1/","1/0", "1 1/1", "1 0/0","1 /","1 /0", "1 0/"};
for (int x = 0 ;x<s.length;x++) {
if(s[x].matches("[0]?([.][0]{1,3}\\s{0,1})?")){
System.out.println(x+") "+s[x]+" ---- Zero");
}
else if(s[x].matches("\\d{0,3}([.]\\d{1,3}\\s{0,1})?")){
System.out.println(x+") "+Float.valueOf(s[x])+" ---- Decimal");
}
else if(s[x].matches("[1-9]{1,5}([.]\\d{1,3})?\\s[1-9]\\d{0,2}([/]\\d{0,3})?")){
System.out.println(x+") "+s[x]+" ---- Mixed Fraction");
}
else if(s[x].matches("[1-9]\\d{0,4}[/]\\d{0,3}")){
System.out.println(x+") "+s[x]+" ---- Fraction");
}
else{
System.out.println(x+") "+s[x]+" ---- Error");
}
}
}
}
答案 0 :(得分：0)
为了展示在多个部分拆分功能时你可以做些什么，我创建了一些代码。请注意，这不是一个明确的（类）设计。
这段代码的优点是你可以用你解析它们的值实际做。提供良好的错误消息也很有用。如果您更加分割main方法，则可以创建一个实时验证值的解析器（例如，如果要验证GUI中的值，则非常有用）。
public class Numbers {
private static final String[] s = new String[]{ "0",".",".0",".01","1.","1.0","1.01", "1 ","1 1","1/2","1/","1/0", "1 1/1", "1 0/0","1 /","1 /0", "1 0/"};
private static final Pattern FRACTION_PATTERN = Pattern.compile("(?:(\\d+)\\s+)?(\\d+)/(\\d+)");
public static void main(String[] args) {
int counter = 0;
for (String value : s) {
counter++;
String trimmedValue = value.trim();
if (isNumber(trimmedValue)) {
System.out.printf("%d) %s ---- Natural number%n", counter, trimmedValue);
continue;
}
boolean parseDecimal = isProbablyDecimal(trimmedValue);
boolean parseFraction = isProbablyFraction(trimmedValue);
if (parseDecimal && parseFraction) {
System.out.printf("%d) %s ---- Error (both decimal & fraction)%n", counter, trimmedValue);
continue;
}
if (parseDecimal) {
if (!trimmedValue.matches("\\d*[.]\\d+")) {
System.out.printf("%d) %s ---- Error (invalid decimal)%n", counter, trimmedValue);
continue;
}
System.out.printf("%d) %s ---- Decimal value%n", counter, trimmedValue);
continue;
}
if (parseFraction) {
Matcher m = FRACTION_PATTERN.matcher(trimmedValue);
if (!m.matches()) {
System.out.printf("%d) %s ---- Error (invalid faction)%n", counter, trimmedValue);
continue;
}
if (Integer.valueOf(m.group(3)) == 0) {
System.out.printf("%d) %s ---- Error (division by zero in fraction)%n", counter, trimmedValue);
continue;
}
if (m.group(1) != null) {
System.out.printf("%d) %s ---- Mixed fraction%n", counter, trimmedValue);
continue;
}
System.out.printf("%d) %s ---- Fraction%n", counter, trimmedValue);
continue;
}
System.out.printf("%d) %s ---- Error (Cannot make bread out of it)%n", counter, trimmedValue);
continue;
}
}
public static boolean isNumber(String value) {
return value.matches("\\d+");
}
public static boolean isProbablyDecimal(String value) {
// note, some countries use comma instead of dot
return value.contains(".");
}
public static boolean isProbablyFraction(String value) {
return value.contains("/");
}
}
输出：
1) 0 ---- Natural number
2) . ---- Error (invalid decimal)
3) .0 ---- Decimal value
4) .01 ---- Decimal value
5) 1. ---- Error (invalid decimal)
6) 1.0 ---- Decimal value
7) 1.01 ---- Decimal value
8) 1 ---- Natural number
9) 1 1 ---- Error (Cannot make bread out of it)
10) 1/2 ---- Fraction
11) 1/ ---- Error (invalid faction)
12) 1/0 ---- Error (division by zero in fraction)
13) 1 1/1 ---- Mixed fraction
14) 1 0/0 ---- Error (division by zero in fraction)
15) 1 / ---- Error (invalid faction)
16) 1 /0 ---- Error (invalid faction)
17) 1 0/ ---- Error (invalid faction)
答案 1 :(得分：0)
试试这个：
\d+\.\d+|\d+\.$|^.0$|\d+/[1-9]+|\d+ \d+/[1-9]+
答案 2 :(得分：0)
这会返回示例的正确值：
^(\d*\.?\d*)\s?(\d+/[1-9]\d*)?$
在Java中，它将是：^(\\d*\\.?\\d*)\\s?(\\d+/[1-9]\\d*)?$