如何将String转换为int?
"1234" → 1234
如何将String转换为int?
"1234" → 1234
当前回答
Google Guava有tryParse(String),如果无法解析字符串,则返回null,例如:
Integer fooInt = Ints.tryParse(fooString);
if (fooInt != null) {
...
}
其他回答
嗯,需要考虑的一个非常重要的点是Integer解析器抛出了Javadoc中所述的NumberFormatException。
int foo;
String StringThatCouldBeANumberOrNot = "26263Hello"; //will throw exception
String StringThatCouldBeANumberOrNot2 = "26263"; //will not throw exception
try {
foo = Integer.parseInt(StringThatCouldBeANumberOrNot);
} catch (NumberFormatException e) {
//Will Throw exception!
//do something! anything to handle the exception.
}
try {
foo = Integer.parseInt(StringThatCouldBeANumberOrNot2);
} catch (NumberFormatException e) {
//No problem this time, but still it is good practice to care about exceptions.
//Never trust user input :)
//Do something! Anything to handle the exception.
}
在尝试从拆分参数中获取整数值或动态解析某些内容时,处理此异常非常重要。
如上所述,Apache Commons的NumberUtils可以做到这一点。如果无法将字符串转换为int,则返回0。
您还可以定义自己的默认值:
NumberUtils.toInt(String str, int defaultValue)
例子:
NumberUtils.toInt("3244", 1) = 3244
NumberUtils.toInt("", 1) = 1
NumberUtils.toInt(null, 5) = 5
NumberUtils.toInt("Hi", 6) = 6
NumberUtils.toInt(" 32 ", 1) = 1 // Space in numbers are not allowed
NumberUtils.toInt(StringUtils.trimToEmpty(" 32 ", 1)) = 32;
String myString = "1234";
int foo = Integer.parseInt(myString);
如果您查看Java文档,您会注意到“陷阱”是此函数可以引发NumberFormatException,您可以处理该异常:
int foo;
try {
foo = Integer.parseInt(myString);
}
catch (NumberFormatException e) {
foo = 0;
}
(此处理方法默认将格式错误的数字设置为0,但如果您愿意,可以执行其他操作。)
或者,您可以使用Guava库中的Ints方法,该方法与Java 8的Optional相结合,为将字符串转换为int提供了一种强大而简洁的方法:
import com.google.common.primitives.Ints;
int foo = Optional.ofNullable(myString)
.map(Ints::tryParse)
.orElse(0)
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));
}
}
}
这是一个完整的程序,所有条件都是正的和负的,不使用库
import java.util.Scanner;
public class StringToInt {
public static void main(String args[]) {
String inputString;
Scanner s = new Scanner(System.in);
inputString = s.nextLine();
if (!inputString.matches("([+-]?([0-9]*[.])?[0-9]+)")) {
System.out.println("Not a Number");
}
else {
Double result2 = getNumber(inputString);
System.out.println("result = " + result2);
}
}
public static Double getNumber(String number) {
Double result = 0.0;
Double beforeDecimal = 0.0;
Double afterDecimal = 0.0;
Double afterDecimalCount = 0.0;
int signBit = 1;
boolean flag = false;
int count = number.length();
if (number.charAt(0) == '-') {
signBit = -1;
flag = true;
}
else if (number.charAt(0) == '+') {
flag = true;
}
for (int i = 0; i < count; i++) {
if (flag && i == 0) {
continue;
}
if (afterDecimalCount == 0.0) {
if (number.charAt(i) - '.' == 0) {
afterDecimalCount++;
}
else {
beforeDecimal = beforeDecimal * 10 + (number.charAt(i) - '0');
}
}
else {
afterDecimal = afterDecimal * 10 + number.charAt(i) - ('0');
afterDecimalCount = afterDecimalCount * 10;
}
}
if (afterDecimalCount != 0.0) {
afterDecimal = afterDecimal / afterDecimalCount;
result = beforeDecimal + afterDecimal;
}
else {
result = beforeDecimal;
}
return result * signBit;
}
}