How to determine whether a string is an int in java

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. .

If you want to learn more related tutorials, you can visit: java introductory programming

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