Java String Compare

In this chapter you will learn:

How to compare two String values
How to compare two string value for equality
What are the difference between equals() and ==

Compare two String values

Here are the two methods we can use to compare two String values.

int compareTo(String anotherString) compares two strings lexicographically.
int compareToIgnoreCase(String str) compares two strings lexicographically, ignoring case differences.

The result of the compareTo(String anotherString) and compareToIgnoreCase(String str) is shown here:

Value	Meaning
Less than zero	The invoking string is less than str.
Greater than zero	The invoking string is greater than str.
Zero	The two strings are equal.

public class Main {
  public static void main(String[] argv) {
    String str = "Demo2s.com";
    String str2 = "demo.com";
    System.out.println(str.compareTo(str2));
    System.out.println(str.compareToIgnoreCase(str2));
// ja  va 2  s. c om
  }
}

The output:

compareToIgnoreCase(String str) returns the same results as compareTo( ). It only ignores the case differences.

public class Main {
//from   j  a  v a 2s.  co  m
  public static void main(String args[]) {
    System.out.println("A".compareToIgnoreCase("a"));
  }
}

The output:

Compare two string value for equality

The following two methods compare string value for equality.

boolean equals(Object anObject) compares this string to the specified object.
boolean equalsIgnoreCase(String anotherString) compares this String to another String, ignoring case considerations.

public class MainClass {
  public static void main(String args[]) {
  String s1 = "Hello";
  String s2 = "Hello";
  String s3 = "Goodbye";
  String s4 = "HELLO";
  System.out.println(s1 + " equals " + s2 + " -> " + s1.equals(s2));
  System.out.println(s1 + " equals " + s3 + " -> " + s1.equals(s3));
  System.out.println(s1 + " equals " + s4 + " -> " + s1.equals(s4));
  }//from j a  v a2 s  .  co m
}

The following code checks the length of a string, then gets the fourth char out of the string object and compares these two string objects.

public class Main {
  public static void main(String args[]) {
    String strOb1 = "demo2s.com";
    String strOb2 = "demo2s.com";
    String strOb3 = strOb1;/* j  a v  a2 s .com*/

    System.out.println("Length of strOb1: " + strOb1.length());
    System.out.println("Char at index 3 in strOb1: " + strOb1.charAt(3));

    if (strOb1.equals(strOb2))
      System.out.println("strOb1 == strOb2");
    else
      System.out.println("strOb1 != strOb2");

    if (strOb1.equals(strOb3))
      System.out.println("strOb1 == strOb3");
    else
      System.out.println("strOb1 != strOb3");
  }
}

This program generates the following output:

The comparison is case-sensitive.

public class Main {
  public static void main(String args[]) {
    String s1 = "Hello";
    String s2 = "Hello";
    String s3 = "Good-bye";
    String s4 = "HELLO";
    System.out.println(s1 + " equals " + s2 + " -> " +
//  ja v a 2 s  .c  o  m
    s1.equals(s2));
    System.out.println(s1 + " equals " + s3 + " -> " + s1.equals(s3));
    System.out.println(s1 + " equals " + s4 + " -> " + s1.equals(s4));
    System.out.println(s1 + " equalsIgnoreCase " + s4 + " -> " 
                          + s1.equalsIgnoreCase(s4));
  }
}

The output:

To compare igoring case, call equalsIgnoreCase(). It has this general form:

boolean equalsIgnoreCase(String str)

str is the String object being compared with the invoking String object. Here is an example that demonstrates equals( ) and equalsIgnoreCase( ):

public class Main {
  public static void main(String args[]) {
    String s1 = "Hello";
    String s2 = "Hello";
    String s3 = "Good-bye";
    String s4 = "HELLO";
    System.out.println(s1 + " equals " + s2 + " -> " +
//j a  v a 2s.c om
    s1.equals(s2));
    System.out.println(s1 + " equals " + s3 + " -> " + s1.equals(s3));
    System.out.println(s1 + " equals " + s4 + " -> " + s1.equals(s4));
    System.out.println(s1 + " equalsIgnoreCase " + s4 + " -> " 
                        + s1.equalsIgnoreCase(s4));
  }
}

The output from the program is shown here:

equals() vs ==

equals( ) method and the == operator perform two different operations. equals( ) method compares the characters inside a String object. The == operator compares two object references to see whether they refer to the same instance.

The following program shows the differences:

public class Main {
  public static void main(String args[]) {
    String s1 = "demo2s.com";
    String s2 = new String(s1);
/* j  a  va  2  s .  c o  m*/
    System.out.println(s1 + " equals " + s2 + " -> " + s1.equals(s2));
    System.out.println(s1 + " == " + s2 + " -> " + (s1 == s2));
  }
}

Here is the output of the preceding example:

Next chapter...

What you will learn in the next chapter:

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