String comparison is a common programming task and Java provides several way to compare two String in Java. String is a special class in Java, String is immutable and It’s used a lot in every single Java program starting from simple test to enterprise Java application. In this Java String compare tutorial we will see different ways to compare two String in Java and find out how they compare String and when to use equals() or compareTo() for comparison etc.
Here are four examples of comparing String in Java
1) String comparison using equals method
2) String comparison using equalsIgnoreCase method
2) String comparison using compareTo method
4) String comparison using compareToIgnoreCase method
We will see String compare Example using each of this method in example section, before that let's get some theory:
This article is in continuation of my earlier post on String e.g. Difference between String and StringBuffer in Java and How to replace String in java using regular expression etc. If you haven’t read them already you may find them useful and worth reading.
Compare two String using equals method in Java
equals()method compare two Strings for content equality. So if two string contains same letters, in same order and in same case they will be equals by equals() method. equals() method is defined in Object class and String class overrides that for character based comparison. Check 5 tips to override equals()method in Java for more details on equals and its implementation. For example for two Strings "Sony" and "Sony", equals() will return true but for "Sony" and "SONY" it will return false.
Compare String using equalsIgnoreCase method in Java
equalsIgnoreCase is more liberal than equals and compare two strings ignoring there case. So if two String contains same characters and in same order despite of there case e.g. lower case, upper case, Capital case or Camel case they will be equal by equalsIgnoreCase.For example "sony" and "SONY" two Strings will be same by equalsIgnoreCase and it will return true but "Sony" and "Samsung" will not be same and it will return false because they don't contain same characters.
Comparing String using compareTo
compareTo are actual comparison method unlike equals()and equalsIgnoreCase() and tell us whether two Strings are lexicographically equal, precedes or follows each other. if you want to sort Strings lexicographically compareTo() method is used. this is also called natural order of String. returns zero if two Strings are same, less than zero if calling string comes before argument string and greater than zero if calling string comes later than argument string as shown in example below. See things to remember while overriding compareTo method in Java for more detail on compareTo method.
Compare String using compareToIgnoreCase
Similar to compareTo() method with ignoring case like equalsIgnoreCase() and return same values as returned by compareTo during String comparison.
Don't use "==" for String comparison
Many Java programmer makes mistake of using "==" for string comparison. "==" just check if two reference variable are pointing two same object in Java heap and since String is immutable in Java and maintained in String pool two String literal refer same String object which gives sense that "==" can be used to compare string which is incorrect. always use equals() method for equality check and compareTo method for actual string comparison.
Another way of comparing String is writing custom Comparator in Java. write your comparison logic in compare() method and than you can use that logic to compare two strings.
These were some common examples of comparing string in Java. Avoid common mistake of using equality operator “==” for comparing String instead always use equals() method.
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