經常會遇到這樣的情況，需要判斷一個字符串是否是一個合法的數，包括整數，小數或者實數。
網上查到很多文章大多是判斷這個字符串是否全為數字，比如下面這段來自StringUtils的代碼，可以看到，13.2這樣的數字實際上會返回false，可是，他的確是一個數字。
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; } 當然，網上還能查到很多其他方式，諸如用正則表達式判斷是否0-9，用字符ascii碼判斷是否是數字以及用Double.parseDouble()是否拋出異常來判斷是否為數字。
事實上，除了最后一種方式能達到我們的要求，其他的都很難真正做到類似的判斷。但是最后一種方式也很難區別出到底是正整數，負整數，正小數還是負小數，而且，捕獲異常的方式實在是有些難看。
基于此原因，我自己寫了一個工具類，專門用作數的檢測，目前能夠檢測正整數，負整數，整數，正小數，負小數，小數以及實數，采用的仍然是正則表達式的方式，當然，如果有遺漏或者錯誤，歡迎聯系我以便更正，同時也歡迎修改或使用這些代碼以便符合你的應用場景。
可以簡單講下正則的思想以便修改，
1. 對于正整數而言，可以帶+號，第一個數字不能為0
2. 對于負整數而言，必須帶負號，第一個數字也不能為0
3. 對于整數而言，實際是由0，正整數和負整數組成的，所以偷個懶用前兩個方法一起判斷
4. 對于正小數而言，可以考帶+號，并考慮兩種情況，第一個數字為0和第一個數字不為0，第一個數字為0時，則小數點后面應該不為0，第一個數字不為0時，小數點后可以為任意數字
5. 對于負小數而言，必須帶負號，其余都同上
6. 對于小數，可以帶正負號，并且帶小數點就行了，但是至少保證小數點有一邊不為空，所以這里還是分左邊不為空和右邊不為空的情況
7. 實數比較簡單，，要么是整數，要么是小數
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); } } 測試用例如下：
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")); } } 以上就是本文的全部內容，希望對大家的學習有所幫助，也希望大家多多支持VEVB武林網。
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