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Str2Int.java
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54 lines (48 loc) · 1.79 KB
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package Chap7;
/**
* 将一个字符串转换成一个整数，要求不能使用字符串转换整数的库函数。
* 数值为0或者字符串不是一个合法的数值则返回0
*/
public class Str2Int {
public static boolean valid;
public static int strToInt(String str) {
valid = false;
if (str == null || str.length() == 0) {
return 0;
}
boolean isNegative = false;
long number = 0;
for (int i = 0; i < str.length(); i++) {
// 第一位是正负号就跳过
if (i == 0 && str.charAt(i) == '+' || str.charAt(i) == '-') {
if (str.charAt(i) == '-') {
isNegative = true;
}
if (str.length() == 1) {
return 0;
}
continue;
}
// 中间有任何字符不是数字直接返回
if (str.charAt(i) < '0' || str.charAt(i) > '9') {
return 0;
}
int flag = isNegative ? -1 : 1;
// '4'的ASCII码就比'0'的ASCII码大4，所以可以减去'0'的ASCII码将字符转数字
number = number * 10 + flag * (str.charAt(i) - '0');
if (!isNegative && number > Integer.MAX_VALUE || isNegative && number < Integer.MIN_VALUE) {
return 0;
}
}
valid = true;
return (int)number;
}
public static void main(String[] args) {
System.out.println(strToInt("12"));
System.out.println(strToInt("-12"));
System.out.println(strToInt("+12"));
System.out.println(strToInt("+")+ " "+ Str2Int.valid);
System.out.println(strToInt("0")+ " "+ Str2Int.valid);
System.out.println(strToInt("12345678901112")+ " "+ Str2Int.valid);
}
}