如何将String转换为int?
"1234" → 1234
如何将String转换为int?
"1234" → 1234
当前回答
使用不同的字符串输入尝试以下代码:
String a = "10";
String a = "10ssda";
String a = null;
String a = "12102";
if(null != a) {
try {
int x = Integer.ParseInt(a.trim());
Integer y = Integer.valueOf(a.trim());
// It will throw a NumberFormatException in case of invalid string like ("10ssda" or "123 212") so, put this code into try catch
} catch(NumberFormatException ex) {
// ex.getMessage();
}
}
其他回答
另一种解决方案是使用Apache Commons的NumberUtils:
int num = NumberUtils.toInt("1234");
Apache实用程序很好,因为如果字符串是无效的数字格式,则始终返回0。因此,节省了try-catch块。
Apache NumberUtils API 3.4版
使用不同的字符串输入尝试以下代码:
String a = "10";
String a = "10ssda";
String a = null;
String a = "12102";
if(null != a) {
try {
int x = Integer.ParseInt(a.trim());
Integer y = Integer.valueOf(a.trim());
// It will throw a NumberFormatException in case of invalid string like ("10ssda" or "123 212") so, put this code into try catch
} catch(NumberFormatException ex) {
// ex.getMessage();
}
}
我有一个解决方案,但我不知道它有多有效。但它工作得很好,我认为你可以改进它。另一方面,我用JUnit做了几次测试,哪一步正确。我附上了功能和测试:
static public Integer str2Int(String str) {
Integer result = null;
if (null == str || 0 == str.length()) {
return null;
}
try {
result = Integer.parseInt(str);
}
catch (NumberFormatException e) {
String negativeMode = "";
if(str.indexOf('-') != -1)
negativeMode = "-";
str = str.replaceAll("-", "" );
if (str.indexOf('.') != -1) {
str = str.substring(0, str.indexOf('.'));
if (str.length() == 0) {
return (Integer)0;
}
}
String strNum = str.replaceAll("[^\\d]", "" );
if (0 == strNum.length()) {
return null;
}
result = Integer.parseInt(negativeMode + strNum);
}
return result;
}
使用JUnit进行测试:
@Test
public void testStr2Int() {
assertEquals("is numeric", (Integer)(-5), Helper.str2Int("-5"));
assertEquals("is numeric", (Integer)50, Helper.str2Int("50.00"));
assertEquals("is numeric", (Integer)20, Helper.str2Int("$ 20.90"));
assertEquals("is numeric", (Integer)5, Helper.str2Int(" 5.321"));
assertEquals("is numeric", (Integer)1000, Helper.str2Int("1,000.50"));
assertEquals("is numeric", (Integer)0, Helper.str2Int("0.50"));
assertEquals("is numeric", (Integer)0, Helper.str2Int(".50"));
assertEquals("is numeric", (Integer)0, Helper.str2Int("-.10"));
assertEquals("is numeric", (Integer)Integer.MAX_VALUE, Helper.str2Int(""+Integer.MAX_VALUE));
assertEquals("is numeric", (Integer)Integer.MIN_VALUE, Helper.str2Int(""+Integer.MIN_VALUE));
assertEquals("Not
is numeric", null, Helper.str2Int("czv.,xcvsa"));
/**
* Dynamic test
*/
for(Integer num = 0; num < 1000; num++) {
for(int spaces = 1; spaces < 6; spaces++) {
String numStr = String.format("%0"+spaces+"d", num);
Integer numNeg = num * -1;
assertEquals(numStr + ": is numeric", num, Helper.str2Int(numStr));
assertEquals(numNeg + ": is numeric", numNeg, Helper.str2Int("- " + numStr));
}
}
}
自定义算法:
public static int toInt(String value) {
int output = 0;
boolean isFirstCharacter = true;
boolean isNegativeNumber = false;
byte bytes[] = value.getBytes();
for (int i = 0; i < bytes.length; i++) {
char c = (char) bytes[i];
if (!Character.isDigit(c)) {
isNegativeNumber = (c == '-');
if (!(isFirstCharacter && (isNegativeNumber || c == '+'))) {
throw new NumberFormatException("For input string \"" + value + "\"");
}
} else {
int number = Character.getNumericValue(c);
output = output * 10 + number;
}
isFirstCharacter = false;
}
if (isNegativeNumber)
output *= -1;
return output;
}
另一种解决方案:
(使用string charAt方法,而不是将字符串转换为字节数组)
public static int toInt(String value) {
int output = 0;
boolean isFirstCharacter = true;
boolean isNegativeNumber = false;
for (int i = 0; i < value.length(); i++) {
char c = value.charAt(i);
if (!Character.isDigit(c)) {
isNegativeNumber = (c == '-');
if (!(isFirstCharacter && (isNegativeNumber || c == '+'))) {
throw new NumberFormatException("For input string \"" + value + "\"");
}
} else {
int number = Character.getNumericValue(c);
output = output * 10 + number;
}
isFirstCharacter = false;
}
if (isNegativeNumber)
output *= -1;
return output;
}
示例:
int number1 = toInt("20");
int number2 = toInt("-20");
int number3 = toInt("+20");
System.out.println("Numbers = " + number1 + ", " + number2 + ", " + number3);
try {
toInt("20 Hadi");
} catch (NumberFormatException e) {
System.out.println("Error: " + e.getMessage());
}
import java.util.*;
public class strToint {
public static void main(String[] args) {
String str = "123";
byte barr[] = str.getBytes();
System.out.println(Arrays.toString(barr));
int result = 0;
for(int i = 0; i < barr.length; i++) {
//System.out.print(barr[i]+" ");
int ii = barr[i];
char a = (char) ii;
int no = Character.getNumericValue(a);
result = result * 10 + no;
System.out.println(result);
}
System.out.println("result:"+result);
}
}