34 lines
1.2 KiB
Java
34 lines
1.2 KiB
Java
package Maths;
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public class ParseInteger {
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public static void main(String[] args) {
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assert parseInt("123") == Integer.parseInt("123");
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assert parseInt("-123") == Integer.parseInt("-123");
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assert parseInt("0123") == Integer.parseInt("0123");
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assert parseInt("+123") == Integer.parseInt("+123");
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}
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/**
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* Parse a string to integer
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*
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* @param s the string
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* @return the integer value represented by the argument in decimal.
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* @throws NumberFormatException if the {@code string} does not contain a parsable integer.
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*/
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public static int parseInt(String s) {
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if (s == null) {
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throw new NumberFormatException("null");
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}
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boolean isNegative = s.charAt(0) == '-';
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boolean isPositive = s.charAt(0) == '+';
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int number = 0;
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for (int i = isNegative ? 1 : isPositive ? 1 : 0, length = s.length(); i < length; ++i) {
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if (!Character.isDigit(s.charAt(i))) {
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throw new NumberFormatException("s=" + s);
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}
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number = number * 10 + s.charAt(i) - '0';
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}
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return isNegative ? -number : number;
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}
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}
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