1. Use the functions that come with JAVA
public static boolean isNumeric(String str){ for (int i = 0; i < str.length(); i++){ System.out.println(str.charAt(i)); if (!Character.isDigit(str.charAt(i))){ return false; } } return true; }
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2. Use regular expressions
First, import java.util.regex.Pattern
and java.util.regex. Matcher
public boolean isNumeric(String str){ Pattern pattern = Pattern.compile("[0-9]*"); Matcher isNum = pattern.matcher(str); if( !isNum.matches() ){ return false; } return true; }
The first method can only verify numbers without the negative sign "-", that is, if you enter a negative number -199, the output result will be false; while the second method can be modified Regular expressions can be used to check negative numbers. Just change the regular expression to "^-?[0-9]" and change it to "-?[0-9].?[0-9]" to match all numbers. .
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