Compare Two Strings in Java - equals, compareTo() methods

If you have to compare two Strings in Java or the portion of two Strings on the basis of the content of those Strings then you can do it using one of the following methods-

equals() method or equalsIgnoreCase() if you don’t want to consider case. See example.
compareTo() method or compareToIgnoreCase() if you don’t want to consider case. See example.
For comparing portion of the String you can use startsWith() and endsWith() methods. See example.
To compare region of one String with the specified region of another String you can use regionMatches() method. See example.

Compare Strings using equals() and equalsIgnoreCase() methods

boolean equals(Object anObject)- Compares this string to the specified object. This method returns true if the passed argument is not null and is a String object having the same sequence of characters as this String.
boolean equalsIgnoreCase(String anotherString)- Compares this String to another String, ignoring case considerations. Two strings are considered equal (ignoring case) if they are of the same length and corresponding characters in the two strings are equal.

Java example using equals() method

public class StringComapre {
  public static void main(String[] args) {
    String str1 = "Hello";
    String str2 = "Hello";
    String str3 = "hello";
    //returns true
    System.out.println("str1.equals(str2)-" + str1.equals(str2));
    //returns false as case is different
    System.out.println("str1.equals(str3)-" + str1.equals(str3));
  }
}

Output

str1.equals(str2)-true
str1.equals(str3)-false

Java example using equalsIgnoreCase() method

public class StringComapre {
  public static void main(String[] args) {
    String str1 = "Hello";
    String str2 = "Hello";
    String str3 = "hello";
    //returns true
    System.out.println("str1.equals(str2)-" + str1.equals(str2));
    //returns true as case is ignored
    System.out.println("str1.equalsIgnoreCase(str3)-" + str1.equalsIgnoreCase(str3));
  }
}

Output

str1.equals(str2)-true
str1.equalsIgnoreCase(str3)-true

Compare Strings using compareTo() and compareToIgnoreCase() methods

int compareTo(String anotherString)- Compares two strings lexicographically. Returns positive integer if this String is greater than the argument, returns negative integer if this String is less than the argument, returns zero if this string is equal to the argument.
int compareToIgnoreCase(String str)- Compares two strings lexicographically, ignoring case differences. Returns positive integer if this String is greater than the argument, returns negative integer if this String is less than the argument, returns zero if this string is equal to the argument, ignoring case considerations.

Java example using compareTo() method

public class StringComapre {
  public static void main(String[] args) {
    String str1 = "Hello";
    String str2 = "Hello";
    String str3 = "Halo";
    // returns 0
    System.out.println("str1.compareTo(str2): " + str1.compareTo(str2));
    // returns positive integer
    System.out.println("str1.compareTo(str3): " + str1.compareTo(str3));
    // returns negative integer
    System.out.println("str3.compareTo(str1): " + str3.compareTo(str1));
  }
}

Output

str1.compareTo(str2): 0
str1.compareTo(str3): 4
str3.compareTo(str1): -4

Since both str1 and str2 have the same value so 0 is returned on comparing them. On comparing str1 with str3 positive integer (4) is returned as "hello" comes after "halo".

Java example using compareToIgnoreCase() method

public class StringComapre {
  public static void main(String[] args) {
    String str1 = "Hello";
    String str2 = "hello";
    String str3 = "cello";
    // returns 0
    System.out.println("str1.compareTo(str2): " + str1.compareToIgnoreCase(str2));
    // returns positive integer
    System.out.println("str1.compareTo(str3): " + str1.compareTo(str3));
    // returns negative integer
    System.out.println("str3.compareTo(str1): " + str3.compareTo(str1));
  }
}

Output

str1.compareTo(str2): 0
str1.compareTo(str3): -27
str3.compareTo(str1): 27

Compare String portions using startsWith() and endsWith() methods

boolean startsWith(String str)- Tests if this string starts with the passed argument. Returns true if substring matches at the start, false otherwise.
boolean startsWith(String str, int toffset)- Tests if the substring of this string beginning at the specified index starts with the passed argument. Returns true if substring matches at the start, false otherwise.
boolean endsWith(String str)- Tests if this string ends with the passed argument. Returns true if substring matches at the end, false otherwise.

Java example using startsWith() and endsWith()

public class StringComapre {
  public static void main(String[] args) {
    String str = "Compare this String";

    // returns true
    System.out.println("str.startsWith(\"Compare\"): " + str.startsWith("Compare"));
    // returns false
    System.out.println("str.startsWith(\"Comparison\"): " + str.startsWith("Comparison"));
    // returns true- Comparison starts from index 8
    System.out.println("str.startsWith(\"this\"): " + str.startsWith("this", 8));
    
    // returns true
    System.out.println("str.endsWith(\"String\"): " + str.endsWith("String"));
    // returns false
    System.out.println("str.endsWith(\"Sting\"): " + str.endsWith("Sting"));
  }
}

Output

str.startsWith("Compare"): true
str.startsWith("Comparison"): false
str.startsWith("this"): true
str.endsWith("String"): true
str.endsWith("Sting"): false

Compare String portions using regionMatches method

boolean regionMatches(int toffset, String other, int ooffset, int len)- Tests if two string regions are equal. A substring of the first string is compared to the substring of the second string. Index from which the substring of the first string starts is specified using toffset. Index from which the substring of the second string starts is specified using ooffset. Length of the substring which is to be compared is specfied using len.
boolean regionMatches(boolean ignoreCase, int toffset, String other, int ooffset, int len)- If ignoreCase is passed as true, ignore case when comparing characters.

public class StringComapre {
  public static void main(String[] args) {
    String str1 = "Compare this string";
    String str2 = "Compare with this String";
    
    // Comparing "this" portion of both Strings- true
    System.out.println("str1.regionMatches(8, str2, 13, 4): " + str1.regionMatches(8, str2, 13, 4));
    // Comparing "String" portion of both Strings- false when case is considered
    System.out.println("str1.regionMatches(13, str2, 18, 6): " + str1.regionMatches(13, str2, 18, 6));
    // Comparing "String" portion of both Strings- true when case is ignored
    System.out.println("str1.regionMatches(true, 13, str2, 18, 6): " + str1.regionMatches(true, 13, str2, 18, 6));
  }
}

Output

str1.regionMatches(8, str2, 13, 4): true
str1.regionMatches(13, str2, 18, 6): false
str1.regionMatches(true, 13, str2, 18, 6): true

That's all for the topic Compare Two Strings in Java - equals, compareTo() methods . If something is missing or you have something to share about the topic please write a comment.

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June 29, 2022