Get integer difference between string just like strcmp

Question

I just need a function that will, for two given strings, return negative, positive or zero value. In C, strcmp is used:

char* a = "Hello";
char* b = "Aargh";

strcmp(a, b);  //-1
strcmp(a, a);  //0
strcmp(b, a);  //1

Does Java have any easy intuitive way to do it, or do I have to use the Comparator interface?

Answer 1

Does Java have any easy intuitive way to do it?

Yes, it does: java.lang.String implements Comparable<String> interface, with compareTo function:

int comparisonResult = a.compareTo(b);

There is also a case-insensitive version:

int comparisonResult = a.compareToIgnoreCase(b);

Answer 2

The String.compareTo method is the way to go in Java.

How to use it :

import java.lang.*;

public class StringDemo {

  public static void main(String[] args) {

    String str1 = "tutorials", str2 = "point";

    // comparing str1 and str2
    int retval = str1.compareTo(str2);

    // prints the return value of the comparison
    if (retval < 0) {
       System.out.println("str1 is less than str2");
    }

    else if (retval == 0) {
       System.out.println("str1 is equal to str2");
    }

    else {
       System.out.println("str1 is greater than str2");
    }
  }
}

Output :

str1 is less than str2

Example taken from : http://www.tutorialspoint.com/java/lang/string_compareto.htm

Answer 3

那compareTo呢？

int value = a.compareTo(b);

Answer 4

You can use compareTo but should include a null check as well if you want to be safe:

if (a != null){
    result = a.compareTo(b);
} else {
    //decide what to do here
}

Answer 5

As it is previously answered, Java has a built-in String.compareTo(String anotherString) method, you should checkout the runtime sources (you should search google for rt.jar ).

However, here is a working sample with same logic applied on the compareTo method;

Method Implementation

public static int stringCompare(String str1, String str2) {
    char[] charArray1 = str1.toCharArray();
    char[] charArray2 = str2.toCharArray();

    int lim = Math.min(charArray1.length, charArray2.length);

    int k = 0;
    while (k < lim) {
        if (charArray1[k] != charArray2[k]) {
            return charArray1[k] - charArray2[k];
        }
        k++;
    }
    return charArray1.length - charArray2.length;
}

Demo Code

public class StringCmp1 {

    public static void main(String[] args) {
        String str1 = "aa";
        String str2 = "ad";

        System.out.println("Comparison of '" + str1 + "' and '" + str2 + "'");
        System.out.println("Custom Method    : " + str1.compareTo(str2));
        System.out.println("Built-in Method  : " + stringCompare(str2, str1));

        System.out.println("\nComparison of '" + str2 + "' and '" + str1 + "'");
        System.out.println("Custom Method    : " + str2.compareTo(str1));
        System.out.println("Built-in Method  : " + stringCompare(str1, str2));
    }

    public static int stringCompare(String str1, String str2) {
        char[] charArray1 = str1.toCharArray();
        char[] charArray2 = str2.toCharArray();

        int lim = Math.min(charArray1.length, charArray2.length);

        int k = 0;
        while (k < lim) {
            if (charArray1[k] != charArray2[k]) {
                return charArray1[k] - charArray2[k];
            }
            k++;
        }
        return charArray1.length - charArray2.length;
    }

}

Output

Comparison of 'aa' and 'ad'
Custom Method    : -3
Built-in Method  : 3

Comparison of 'ad' and 'aa'
Custom Method    : 3
Built-in Method  : -3