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判断是否是整数,小数或实数

    经常会遇到这样的情况,需要判断一个字符串是否是一个合法的数,包括整数,小数或者实数。

    网上查到很多文章大多是判断这个字符串是否全为数字,比如下面这段来自StringUtils的代码,可以看到,13.2这样的数字实际上会返回false,可是,他的确是一个数字。

public static boolean isNumeric(String str) {         if (str == null) {             return false;         }         int sz = str.length();         for (int i = 0; i < sz; i++) {             if (Character.isDigit(str.charAt(i)) == false) {                 return false;             }         }         return true;     }

   当然,网上还能查到很多其他方式,诸如用正则表达式判断是否0-9,用字符ascii码判断是否是数字以及用Double.parseDouble()是否抛出异常来判断是否为数字。

   事实上,除了最后一种方式能达到我们的要求,其他的都很难真正做到类似的判断。但是最后一种方式也很难区别出到底是正整数,负整数,正小数还是负小数,而且,捕获异常的方式实在是有些难看。

   基于此原因,我自己写了一个工具类,专门用作数的检测,目前能够检测正整数,负整数,整数,正小数,负小数,小数以及实数,采用的仍然是正则表达式的方式,当然,如果有遗漏或者错误,欢迎联系我以便更正,同时也欢迎修改或使用这些代码以便符合你的应用场景。

   可以简单讲下正则的思想以便修改,

   1. 对于正整数而言,可以带+号,第一个数字不能为0

   2. 对于负整数而言,必须带负号,第一个数字也不能为0

   3. 对于整数而言,实际是由0,正整数和负整数组成的,所以偷个懒用前两个方法一起判断

   4. 对于正小数而言,可以考带+号,并考虑两种情况,第一个数字为0和第一个数字不为0,第一个数字为0时,则小数点后面应该不为0,第一个数字不为0时,小数点后可以为任意数字

   5. 对于负小数而言,必须带负号,其余都同上

   6. 对于小数,可以带正负号,并且带小数点就行了,但是至少保证小数点有一边不为空,所以这里还是分左边不为空和右边不为空的情况

   7. 实数比较简单,,要么是整数,要么是小数

package com.sap.cesp.creditinsight.web.app.util;  import java.util.regex.Matcher; import java.util.regex.Pattern;  public class NumberValidationUtils { 	 	private static boolean isMatch(String regex, String orginal){ 		if (orginal == null || orginal.trim().equals("")) {             return false;         } 		Pattern pattern = Pattern.compile(regex); 		Matcher isNum = pattern.matcher(orginal); 		return isNum.matches(); 	}  	public static boolean isPositiveInteger(String orginal) { 		return isMatch("^\+{0,1}[1-9]\d*", orginal); 	}  	public static boolean isNegativeInteger(String orginal) { 		return isMatch("^-[1-9]\d*", orginal); 	}  	public static boolean isWholeNumber(String orginal) { 		return isMatch("[+-]{0,1}0", orginal) || isPositiveInteger(orginal) || isNegativeInteger(orginal); 	} 	 	public static boolean isPositiveDecimal(String orginal){ 		return isMatch("\+{0,1}[0]\.[1-9]*|\+{0,1}[1-9]\d*\.\d*", orginal); 	} 	 	public static boolean isNegativeDecimal(String orginal){ 		return isMatch("^-[0]\.[1-9]*|^-[1-9]\d*\.\d*", orginal); 	} 	 	public static boolean isDecimal(String orginal){ 		return isMatch("[-+]{0,1}\d+\.\d*|[-+]{0,1}\d*\.\d+", orginal); 	} 	 	public static boolean isRealNumber(String orginal){ 		return isWholeNumber(orginal) || isDecimal(orginal); 	}  } 

测试用例如下:

package com.sap.cesp.creditinsight.web.app.util;  import junit.framework.Assert;  import org.junit.Test;  public class NumberValidationUtilsTest {  	/** 	 * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isPositiveInteger(java.lang.String)} 	 */ 	//correct test case: 1, 87653521123567 	//wrong test case: 0.1, 0, 0123, -1, -0.1, ab 	@Test 	public void testIsPositiveInteger() { 		Assert.assertTrue(NumberValidationUtils.isPositiveInteger("1")); 		Assert.assertTrue(NumberValidationUtils.isPositiveInteger("+12")); 		Assert.assertTrue(NumberValidationUtils.isPositiveInteger("87653521123567")); 		Assert.assertFalse(NumberValidationUtils.isPositiveInteger("0.1")); 		Assert.assertFalse(NumberValidationUtils.isPositiveInteger("0")); 		Assert.assertFalse(NumberValidationUtils.isPositiveInteger("0123")); 		Assert.assertFalse(NumberValidationUtils.isPositiveInteger("-1")); 		Assert.assertFalse(NumberValidationUtils.isPositiveInteger("-0.1")); 		Assert.assertFalse(NumberValidationUtils.isPositiveInteger("ab")); 	}  	/** 	 * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isNegativeInteger(java.lang.String)} 	 */ 	//correct test case: -1, -87653521123567 	//wrong test case: 0.1, 0, 0123, 1, -0.1, -ab 	@Test 	public void testIsNegativeInteger() { 		Assert.assertTrue(NumberValidationUtils.isNegativeInteger("-1")); 		Assert.assertTrue(NumberValidationUtils.isNegativeInteger("-87653521123567")); 		Assert.assertFalse(NumberValidationUtils.isNegativeInteger("0.1")); 		Assert.assertFalse(NumberValidationUtils.isNegativeInteger("0")); 		Assert.assertFalse(NumberValidationUtils.isNegativeInteger("0123")); 		Assert.assertFalse(NumberValidationUtils.isNegativeInteger("1")); 		Assert.assertFalse(NumberValidationUtils.isNegativeInteger("-0.1")); 		Assert.assertFalse(NumberValidationUtils.isNegativeInteger("ab")); 	}  	/** 	 * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isWholeNumber(java.lang.String)}. 	 */ 	//correct test case: -1, 0, 1, 8673434231, -282464334 	//wrong test case: 0.1, 0123, -0.1, ab 	@Test 	public void testIsWholeNumber() { 		Assert.assertTrue(NumberValidationUtils.isWholeNumber("-1")); 		Assert.assertTrue(NumberValidationUtils.isWholeNumber("0")); 		Assert.assertTrue(NumberValidationUtils.isWholeNumber("1")); 		Assert.assertTrue(NumberValidationUtils.isWholeNumber("+12")); 		Assert.assertTrue(NumberValidationUtils.isWholeNumber("8673434231")); 		Assert.assertTrue(NumberValidationUtils.isWholeNumber("-282464334")); 		Assert.assertFalse(NumberValidationUtils.isWholeNumber("0123")); 		Assert.assertFalse(NumberValidationUtils.isWholeNumber("0.1")); 		Assert.assertFalse(NumberValidationUtils.isWholeNumber("-0.1")); 		Assert.assertFalse(NumberValidationUtils.isWholeNumber("ab")); 	}  	/** 	 * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isPositiveDecimal(java.lang.String)} 	 */ 	//correct test case: 0.1, 0.132213, 1.0 	//wrong test case: 1, 0.0, 0123, -1, -0.1 	@Test 	public void testIsPositiveDecimal() { 		Assert.assertTrue(NumberValidationUtils.isPositiveDecimal("0.1")); 		Assert.assertTrue(NumberValidationUtils.isPositiveDecimal("0.132213")); 		Assert.assertTrue(NumberValidationUtils.isPositiveDecimal("30.00")); 		Assert.assertTrue(NumberValidationUtils.isDecimal("0.")); 		Assert.assertTrue(NumberValidationUtils.isPositiveDecimal("+12.0")); 		Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("0123")); 		Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("1")); 		Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("0.0")); 		Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("ab")); 		Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("-1")); 		Assert.assertFalse(NumberValidationUtils.isPositiveDecimal("-0.1")); 	}  	/** 	 * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isNegativeDecimal(java.lang.String)} 	 */ 	//correct test case: -0.132213, -1.0 	//wrong test case: 1, 0, 0123, -1, 0.1 	@Test 	public void testIsNegativeDecimal() { 		Assert.assertTrue(NumberValidationUtils.isNegativeDecimal("-0.132213")); 		Assert.assertTrue(NumberValidationUtils.isNegativeDecimal("-1.0")); 		Assert.assertTrue(NumberValidationUtils.isDecimal("-0.")); 		Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("1")); 		Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("0")); 		Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("0123")); 		Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("0.0")); 		Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("ab")); 		Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("-1")); 		Assert.assertFalse(NumberValidationUtils.isNegativeDecimal("0.1")); 	}  	/** 	 * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isDecimal(java.lang.String)}. 	 */ 	//correct test case: 0.1, 0.00, -0.132213 	//wrong test case: 1, 0, 0123, -1,  0., ba 	@Test 	public void testIsDecimal() { 		Assert.assertTrue(NumberValidationUtils.isDecimal("0.1")); 		Assert.assertTrue(NumberValidationUtils.isDecimal("0.00")); 		Assert.assertTrue(NumberValidationUtils.isDecimal("+0.0")); 		Assert.assertTrue(NumberValidationUtils.isDecimal("-0.132213")); 		Assert.assertTrue(NumberValidationUtils.isDecimal("0.")); 		Assert.assertFalse(NumberValidationUtils.isDecimal("1")); 		Assert.assertFalse(NumberValidationUtils.isDecimal("0123")); 		Assert.assertFalse(NumberValidationUtils.isDecimal("0")); 		Assert.assertFalse(NumberValidationUtils.isDecimal("ab")); 		Assert.assertFalse(NumberValidationUtils.isDecimal("-1")); 		 	}  	/** 	 * Test method for {@link com.sap.cesp.creditinsight.web.app.util.NumberValidationUtils#isRealNumber(java.lang.String)}. 	 */ 	//correct test case: 0.032213, -0.234, 0.0, 1, -1, 0 	//wrong test case: 00.13, ab, +0.14 	@Test 	public void testIsRealNumber() { 		Assert.assertTrue(NumberValidationUtils.isRealNumber("0.032213")); 		Assert.assertTrue(NumberValidationUtils.isRealNumber("-0.234")); 		Assert.assertTrue(NumberValidationUtils.isRealNumber("0.0")); 		Assert.assertTrue(NumberValidationUtils.isRealNumber("1")); 		Assert.assertTrue(NumberValidationUtils.isRealNumber("+0.14")); 		Assert.assertTrue(NumberValidationUtils.isRealNumber("-1")); 		Assert.assertTrue(NumberValidationUtils.isRealNumber("0.0")); 		Assert.assertFalse(NumberValidationUtils.isRealNumber("00.13")); 		Assert.assertFalse(NumberValidationUtils.isRealNumber("ab")); 		 	}  } 

    float和double在内存中的表示方式: http://www.360doc.com/content/12/0328/22/8265633_198759107.shtml

    浮点数在计算机中怎么表示:http://www.ruanyifeng.com/blog/2010/06/ieee_floating-point_representation.html

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判断是否是整数,小数或实数 判断是否是整数,小数或实数
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原文始发于:判断是否是整数,小数或实数

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