CODEWITHSUNDEEP
javaarrays
user25976
user25976

Reputation: 1035

find substring index in array using Java

I would like to return the index of a user-input substring from a Character array using Java. The array is initialized, scrambled, then searched. I'm new to this and have tried two different approaches with no success. What am I overlooking? Thanks in advance.

Approach 1:

import java.lang.Math;
import java.util.Scanner;
import java.util.Arrays;
import java.util.List;
import java.util.Collections;

public class ArrayRandomChar {
public static void main(String[] args) {
    // Create an array of characters:
    Character[] anArray = {'P', 'A', 'P', 'A', 'B', 'E', 'A', 'R'};
    for (char ch: anArray)
    System.out.print(ch + " ");
    System.out.println();

    // Create list from array and shuffle
    List<Character> aList = Arrays.asList(anArray);
    Collections.shuffle(aList);
    System.out.print(aList);
    System.out.println();

    // Bring back into array
    Object ob[] = aList.toArray();
    for (Object ch: anArray)
    System.out.print((Character) ch + " ");

    // User input
    Scanner input = new Scanner(System.in);
    String letter = input.next();
    System.out.println(letter);

    // Return index of letter, -1 if doesn't contain
    int retval = aList.IndexOf(letter);
    System.out.println(retval);

    }
      }

Issue: when running document and inputting a letter, -1 is returned even if the list contains the letter.

Approach 2:

public class ArrayRandomChar {
public static void main(String[] args) {

    // Create an array of characters:
    Character[] anArray = {'P', 'A', 'P', 'A', 'B', 'E', 'A', 'R'};
    for (char ch: anArray)
        System.out.print(ch + " ");
    System.out.println();

    // Create list from array:
    List<Character> aList = Arrays.asList(anArray);
    Collections.shuffle(aList);
    System.out.print(aList);
    System.out.println();

    //create array from list
    Object ob[] = aList.toArray();
    for (Object ch: anArray)
        System.out.print((Character) ch + " ");

    //user input
    Scanner input = new Scanner(System.in);
    String letter = input.next();
    int index = Arrays.binarySearch(anArray, letter);
    System.out.println(~index);
    System.out.println(letter);

    }
      }

This throws exception:

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Character
at java.lang.Character.compareTo(Character.java:101)
at java.util.Arrays.binarySearch0(Arrays.java:2001)
at java.util.Arrays.binarySearch(Arrays.java:1943)
at ArrayRandomChar.main(ArrayRandomChar.java:32)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at edu.rice.cs.drjava.model.compiler.JavacCompiler.runCommand(JavacCompiler.java:272)

Upvotes: 3

Views: 2448

Answers (2)

Abhishek Nayak
Abhishek Nayak

Reputation: 3748

Approach 1:

when running document and inputting a letter, -1 is returned even if the list contains the letter.

ok, this problems @Dileep has already answered,

int retval = aList.IndexOf(letter);

Mistake is that you have passed a String type to List.indexOf(Object o) were, aList contains all elements of type Character. So List.indexOf() will always return -1.

you may change to work:

int retval = aList.indexOf(Character.toUpperCase(letter.charAt(0)));

Note: Character.toUpperCase() i have used because you have all elements in upper case.

Approach 2:

throws 

java.lang.ClassCastException: java.lang.String cannot be cast to java.lang.Character

exception message has already answered, that String cannot be a changed/cast to Character, 

int index = Arrays.binarySearch(anArray, letter);

Here,

  • anArray contains elements type of Character

  • you have passed a String to Arrays.binarySearch(), instead of a char or Character, internally when Arrays#binarySearch() invokes Character.compareTo(T o) here, the specified object's type(i.e. letter#String) prevents it from being compared to Character object. then the ClassCastException is throwed.

Solution:

int index = Arrays.binarySearch(anArray, Character.toUpperCase(letter.charAt(0)));

Upvotes: 1

Dileep
Dileep

Reputation: 5440

This will solve the issue..

Approach 1:

int retval = aList.indexOf(letter.charAt(0));

Approach 2:

int index = Arrays.binarySearch(anArray, letter.charAt(0));

The problem is that you are having a character Array aList, and the letter is a String and hence it search for a String in the Character array. Which can possibly cause ClassCastException or String not found.

In short : Character A is not same as String A

Upvotes: 4

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