private static Pattern p = Pattern.compile("^[0-9]*$");

public static boolean isNumeric(String strNum) {
    if (strNum == null) {
        return false;
    }
    return p.matcher(strNum).find();
}

String text="hello 123";
if(Pattern.matches([0-9]+))==true
System.out.println("String"+text);

异常开销很大，但在这种情况下，RegEx需要更长的时间。下面的代码显示了两个函数的简单测试——一个使用异常，一个使用正则表达式。在我的机器上，RegEx版本比异常慢10倍。

import java.util.Date;


public class IsNumeric {

public static boolean isNumericOne(String s) {
    return s.matches("-?\\d+(\\.\\d+)?");  //match a number with optional '-' and decimal.      
}

public static boolean isNumericTwo(String s) {
    try {
        Double.parseDouble(s);
        return true;
    } catch (Exception e) {
        return false;
    }
}

public static void main(String [] args) {

    String test = "12345.F";

    long before = new Date().getTime();     
    for(int x=0;x<1000000;++x) {
        //isNumericTwo(test);
        isNumericOne(test);
    }
    long after = new Date().getTime();

    System.out.println(after-before);

}

}

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;
    }
}

这里有两种可能有效的方法。(不使用异常)。 注意:Java默认是值传递，String的值是String对象数据的地址。 所以，当你在做

stringNumber = stringNumber.replaceAll(" ", "");

您已将输入值更改为没有空格。 如果你愿意，可以去掉这条线。

private boolean isValidStringNumber(String stringNumber)
{
    if(stringNumber.isEmpty())
    {
        return false;
    }

    stringNumber = stringNumber.replaceAll(" ", "");

    char [] charNumber = stringNumber.toCharArray();
    for(int i =0 ; i<charNumber.length ;i++)
    {
        if(!Character.isDigit(charNumber[i]))
        {
            return false;
        }
    }
    return true;
}

这里是另一个方法，以防你想允许浮动 据称，这种方法允许表单中的数字通过 1123123123123123年.123 我刚做好，我想还需要进一步测试以确保它能正常工作。

private boolean isValidStringTrueNumber(String stringNumber)
{
    if(stringNumber.isEmpty())
    {
        return false;
    }

    stringNumber = stringNumber.replaceAll(" ", "");
    int countOfDecimalPoint = 0;
    boolean decimalPointPassed = false;
    boolean commaFound = false;
    int countOfDigitsBeforeDecimalPoint = 0;
    int countOfDigitsAfterDecimalPoint =0 ;
    int commaCounter=0;
    int countOfDigitsBeforeFirstComma = 0;

    char [] charNumber = stringNumber.toCharArray();
    for(int i =0 ; i<charNumber.length ;i++)
    {
        if((commaCounter>3)||(commaCounter<0))
        {
            return false;
        }
        if(!Character.isDigit(charNumber[i]))//Char is not a digit.
        {
            if(charNumber[i]==',')
            {
                if(decimalPointPassed)
                {
                    return false;
                }
                commaFound = true;
                //check that next three chars are only digits.
                commaCounter +=3;
            }
            else if(charNumber[i]=='.')
            {
                decimalPointPassed = true;
                countOfDecimalPoint++;
            }
            else
            {
                return false;
            }
        }
        else //Char is a digit.
        {
            if ((commaCounter>=0)&&(commaFound))
            {
                if(!decimalPointPassed)
                {
                    commaCounter--;
                }
            }

            if(!commaFound)
            {
                countOfDigitsBeforeFirstComma++;
            }

            if(!decimalPointPassed)
            {
                countOfDigitsBeforeDecimalPoint++;
            }
            else
            {
                countOfDigitsAfterDecimalPoint++;
            }
        }
    }
    if((commaFound)&&(countOfDigitsBeforeFirstComma>3))
    {
        return false;
    }
    if(countOfDecimalPoint>1)
    {
        return false;
    }

    if((decimalPointPassed)&&((countOfDigitsBeforeDecimalPoint==0)||(countOfDigitsAfterDecimalPoint==0)))
    {
        return false;
    }
    return true;
}

// only int
public static boolean isNumber(int num) 
{
    return (num >= 48 && c <= 57); // 0 - 9
}

// is type of number including . - e E 
public static boolean isNumber(String s) 
{
    boolean isNumber = true;
    for(int i = 0; i < s.length() && isNumber; i++) 
    {
        char c = s.charAt(i);
        isNumber = isNumber & (
            (c >= '0' && c <= '9') || (c == '.') || (c == 'e') || (c == 'E') || (c == '')
        );
    }
    return isInteger;
}

// is type of number 
public static boolean isInteger(String s) 
{
    boolean isInteger = true;
    for(int i = 0; i < s.length() && isInteger; i++) 
    {
        char c = s.charAt(i);
        isInteger = isInteger & ((c >= '0' && c <= '9'));
    }
    return isInteger;
}

public static boolean isNumeric(String s) 
{
    try
    {
        Double.parseDouble(s);
        return true;
    }
    catch (Exception e) 
    {
        return false;
    }
}