Member Avatar for Samik_1

Error : java.lang.String cannot be converted to String

import java.util.*;
class String

    String str;
    String newstr;
    void inputString()
    {
        Scanner sc = new Scanner(System.in);
        System.out.println("Enter a string:");
        str = sc.nextLine();
    }
    void checkFrequency()
    {
        int freq = 0;
        System.out.println("CHARCTER    FREQUENCY");
        if(str.isUpperCase)
        {
            char []sArray = new String[str.length - 1];
            for(int i = 0; i<= str.length() - 1; i++)
            {
                sArray[i] = str.charAt[i];
            }
            char temp;
            for(int i = 0; i <= Array.length - 2; i++)
            {
                for(int i = 0; i <= sArray.length - 2; i++) 
                if(sArray[j] > sArray[j + 1]);
                {
                    temp = sArray[j];
                    sArray[j] = sArray[j + 1];
                    sArray[j + 1] = temp;
                }
            }
            for(int i = 0; i<= sArray.length - 1; i++)
            {
                if(exists(sArray[i]))
                freq++;
                else
                {
                    newstr = newstr + sArray[i];
                    freq++;
                }
                System.out.println(sArray[i] + freq);
                freq = 0;
            }
            }
    }
    boolean exists(char a)
    {
        for(int i = 0; i <= newstr.length() - 1; i++)
        {
            if(newstr.charAt(i) == a)
            return true;
        }
        return false;
    }
    static void main()
    {
        String obj = new String();
        obj.inputString();
        obj.checkFrequency();
    }
}
  • 2 Contributors
  • 1 Reply
  • 119 Views
  • 58 Minutes Discussion Span
  • Latest Post Latest Post by stultuske

Dani AI

Generated

The immediate compile error comes from naming a user class String, which hides java.lang.String. As noted, that makes String str = sc.nextLine(); try to assign a java.lang.String to the user-defined String type, hence the message "java.lang.String cannot be converted to String". Renaming the class (for example to CharFrequency) is the clean fix; qualifying every variable as java.lang.String is only a stopgap.

Several other problems in the posted code will prevent it from compiling or working correctly:

  • Missing class brace and an incorrect main signature (public static void main(String[] args) is needed to run from the JVM).
  • Confusing String methods and Character helpers (there is no String.isUpperCase; use Character.isUpperCase(char)).
  • Wrong array construction and indexing (char[] should be allocated with new char[str.length()]; charAt is a method: str.charAt(i)).
  • Loop bounds and reuse of the same loop variable in nested loops lead to logic bugs; prefer < length rather than <= length - 1.
  • A stray semicolon after if and references to Array.length (should be sArray.length) break control flow.
  • newstr is never initialized before concatenation, causing a NullPointerException at runtime.

A simpler, robust approach is to avoid manual sorting and count with a map. Example:

public class CharFrequency {
    public static void main(String[] args) {
        java.util.Scanner sc = new java.util.Scanner(System.in);
        java.lang.String input = sc.nextLine();
        java.util.Map<Character,Integer> freq = new java.util.LinkedHashMap<>();
        for (char c : input.toCharArray()) {
            if (Character.isWhitespace(c)) continue;
            freq.put(c, freq.getOrDefault(c, 0) + 1);
        }
        freq.forEach((ch, count) -> System.out.println(ch + "    " + count));
        sc.close();
    }
}

Troubleshooting tips: fix one compiler error at a time, use an IDE or javac to reveal exact line errors, initialize variables, and run small examples (e.g., str.toCharArray() + Arrays.sort) before adding more logic. Refer back to ’s advice to avoid naming collisions with core Java classes.

Member Avatar for stultuske

that's because you've named your own class String, which is a very bad idea.

class String
    String str;
    String newstr;

first of all, you're missing a { there, which means that this is not the actual code you are trying.

try this:

class String{
    java.lang.String str;
    java.lang.String newstr;

otherwise the compiler will assume you meant to use your own String class.
anyway, better sollution: give your class another name

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