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)); } }
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以上就是判断是否是整数，小数或实数正则有哪些写法的详细内容。