在解析字符串之前,如何检查它是否是一个数字?
当前回答
正则表达式匹配
这里是另一个例子升级了“CraigTP”正则表达式匹配更多的验证。
public static boolean isNumeric(String str)
{
return str.matches("^(?:(?:\\-{1})?\\d+(?:\\.{1}\\d+)?)$");
}
只有一个负号——允许且必须在开头。 负号后面必须有数字。 只有一个小数符号。允许的。 小数点后必须有数字。
正则表达式测试
1 -- **VALID**
1. -- INVALID
1.. -- INVALID
1.1 -- **VALID**
1.1.1 -- INVALID
-1 -- **VALID**
--1 -- INVALID
-1. -- INVALID
-1.1 -- **VALID**
-1.1.1 -- INVALID
其他回答
解析它(即使用Integer#parseInt)并简单地捕获异常。=)
澄清一下:parseInt函数检查它是否可以在任何情况下解析该数字(显然),如果您想无论如何都要解析它,那么实际进行解析不会对性能造成任何影响。
如果您不想解析它(或者很少解析它),当然您可能希望采用不同的方法。
这是我对这个问题的回答。
一个方便的方法,你可以使用任何类型的解析器来解析任何字符串:isParsable(对象解析器,字符串str)。解析器可以是Class或对象。这也将允许你使用你写的自定义解析器,应该适用于任何场景,例如:
isParsable(Integer.class, "11");
isParsable(Double.class, "11.11");
Object dateFormater = new java.text.SimpleDateFormat("yyyy.MM.dd G 'at' HH:mm:ss z");
isParsable(dateFormater, "2001.07.04 AD at 12:08:56 PDT");
下面是我的代码和方法描述。
import java.lang.reflect.*;
/**
* METHOD: isParsable<p><p>
*
* This method will look through the methods of the specified <code>from</code> parameter
* looking for a public method name starting with "parse" which has only one String
* parameter.<p>
*
* The <code>parser</code> parameter can be a class or an instantiated object, eg:
* <code>Integer.class</code> or <code>new Integer(1)</code>. If you use a
* <code>Class</code> type then only static methods are considered.<p>
*
* When looping through potential methods, it first looks at the <code>Class</code> associated
* with the <code>parser</code> parameter, then looks through the methods of the parent's class
* followed by subsequent ancestors, using the first method that matches the criteria specified
* above.<p>
*
* This method will hide any normal parse exceptions, but throws any exceptions due to
* programmatic errors, eg: NullPointerExceptions, etc. If you specify a <code>parser</code>
* parameter which has no matching parse methods, a NoSuchMethodException will be thrown
* embedded within a RuntimeException.<p><p>
*
* Example:<br>
* <code>isParsable(Boolean.class, "true");<br>
* isParsable(Integer.class, "11");<br>
* isParsable(Double.class, "11.11");<br>
* Object dateFormater = new java.text.SimpleDateFormat("yyyy.MM.dd G 'at' HH:mm:ss z");<br>
* isParsable(dateFormater, "2001.07.04 AD at 12:08:56 PDT");<br></code>
* <p>
*
* @param parser The Class type or instantiated Object to find a parse method in.
* @param str The String you want to parse
*
* @return true if a parse method was found and completed without exception
* @throws java.lang.NoSuchMethodException If no such method is accessible
*/
public static boolean isParsable(Object parser, String str) {
Class theClass = (parser instanceof Class? (Class)parser: parser.getClass());
boolean staticOnly = (parser == theClass), foundAtLeastOne = false;
Method[] methods = theClass.getMethods();
// Loop over methods
for (int index = 0; index < methods.length; index++) {
Method method = methods[index];
// If method starts with parse, is public and has one String parameter.
// If the parser parameter was a Class, then also ensure the method is static.
if(method.getName().startsWith("parse") &&
(!staticOnly || Modifier.isStatic(method.getModifiers())) &&
Modifier.isPublic(method.getModifiers()) &&
method.getGenericParameterTypes().length == 1 &&
method.getGenericParameterTypes()[0] == String.class)
{
try {
foundAtLeastOne = true;
method.invoke(parser, str);
return true; // Successfully parsed without exception
} catch (Exception exception) {
// If invoke problem, try a different method
/*if(!(exception instanceof IllegalArgumentException) &&
!(exception instanceof IllegalAccessException) &&
!(exception instanceof InvocationTargetException))
continue; // Look for other parse methods*/
// Parse method refuses to parse, look for another different method
continue; // Look for other parse methods
}
}
}
// No more accessible parse method could be found.
if(foundAtLeastOne) return false;
else throw new RuntimeException(new NoSuchMethodException());
}
/**
* METHOD: willParse<p><p>
*
* A convienence method which calls the isParseable method, but does not throw any exceptions
* which could be thrown through programatic errors.<p>
*
* Use of {@link #isParseable(Object, String) isParseable} is recommended for use so programatic
* errors can be caught in development, unless the value of the <code>parser</code> parameter is
* unpredictable, or normal programtic exceptions should be ignored.<p>
*
* See {@link #isParseable(Object, String) isParseable} for full description of method
* usability.<p>
*
* @param parser The Class type or instantiated Object to find a parse method in.
* @param str The String you want to parse
*
* @return true if a parse method was found and completed without exception
* @see #isParseable(Object, String) for full description of method usability
*/
public static boolean willParse(Object parser, String str) {
try {
return isParsable(parser, str);
} catch(Throwable exception) {
return false;
}
}
private static Pattern p = Pattern.compile("^[0-9]*$");
public static boolean isNumeric(String strNum) {
if (strNum == null) {
return false;
}
return p.matcher(strNum).find();
}
下面是用于检查字符串是否为数字的类。它还修复数值字符串:
特点:
删除不必要的零["12.0000000" -> "12"] 删除不必要的零["12.0580000" -> "12.058"] 删除非数字字符["12.00sdfsdf00" -> "12"] 处理负字符串值["-12,020000" -> "-12.02"] 删除多个点["-12.0.20.000" -> "-12.02"] 没有额外的库,只有标准Java
给你…
public class NumUtils {
/**
* Transforms a string to an integer. If no numerical chars returns a String "0".
*
* @param str
* @return retStr
*/
static String makeToInteger(String str) {
String s = str;
double d;
d = Double.parseDouble(makeToDouble(s));
int i = (int) (d + 0.5D);
String retStr = String.valueOf(i);
System.out.printf(retStr + " ");
return retStr;
}
/**
* Transforms a string to an double. If no numerical chars returns a String "0".
*
* @param str
* @return retStr
*/
static String makeToDouble(String str) {
Boolean dotWasFound = false;
String orgStr = str;
String retStr;
int firstDotPos = 0;
Boolean negative = false;
//check if str is null
if(str.length()==0){
str="0";
}
//check if first sign is "-"
if (str.charAt(0) == '-') {
negative = true;
}
//check if str containg any number or else set the string to '0'
if (!str.matches(".*\\d+.*")) {
str = "0";
}
//Replace ',' with '.' (for some european users who use the ',' as decimal separator)
str = str.replaceAll(",", ".");
str = str.replaceAll("[^\\d.]", "");
//Removes the any second dots
for (int i_char = 0; i_char < str.length(); i_char++) {
if (str.charAt(i_char) == '.') {
dotWasFound = true;
firstDotPos = i_char;
break;
}
}
if (dotWasFound) {
String befDot = str.substring(0, firstDotPos + 1);
String aftDot = str.substring(firstDotPos + 1, str.length());
aftDot = aftDot.replaceAll("\\.", "");
str = befDot + aftDot;
}
//Removes zeros from the begining
double uglyMethod = Double.parseDouble(str);
str = String.valueOf(uglyMethod);
//Removes the .0
str = str.replaceAll("([0-9])\\.0+([^0-9]|$)", "$1$2");
retStr = str;
if (negative) {
retStr = "-"+retStr;
}
return retStr;
}
static boolean isNumeric(String str) {
try {
double d = Double.parseDouble(str);
} catch (NumberFormatException nfe) {
return false;
}
return true;
}
}
如果字符串可能包含小数,则可以使用BigDecimal:
try {
new java.math.BigInteger(testString);
} catch(NumberFormatException e) {
throw new RuntimeException("Not a valid number");
}
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