HOW DO I COMPARE STRINGS IN JAVA?

Samuel Fernandes

Total Post:159

Points:1117
Posted by  Samuel Fernandes
Java  String 
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I've been using the == operator in my program to compare all my strings so far. However, I ran into a bug, changed one of them into .equals() instead, and it fixed the bug.

Is == bad? When should it and should it not be used? What's the difference?
  1. Mayank Tripathi

    Post:397

    Points:3117
    Re: How do I compare strings in Java?

    == tests for reference equality.

    .equals() tests for value equality.

    Consequently, if you actually want to test whether two strings have the same value you should use .equals().

    There are however a few situations where you can guarantee that two strings with the same value will be represented by the same object because of String interning. Those cases are specified by the Java Language Specification.

    == is for testing whether two strings are the same object.

    // These two have the same value
    new String("test").equals("test") // --> true 
    // ... but they are not the same object
    new String("test") == "test" // --> false 
    // ... neither are these
    new String("test") == new String("test") // --> false 
    // ... but these are because literals are interned by 
    // the compiler and thus refer to the same object
    "test" == "test" // --> true 
    // concatenation of string literals happens at compile time,
    // also resulting in the same object
    "test" == "te" + "st" // --> true
    // but .substring() is invoked at runtime, generating distinct objects
    "test" == "!test".substring(1) // --> false
    // interned strings can also be recalled by calling .intern()
    "test" == "!test".substring(1).intern() // --> true
    It is important to note that == is a bit cheaper than equals() (a single reference comparison instead of a method call), thus, in situations where it is applicable (i.e. you can guarantee that you are only dealing with interned strings) it can present an important performance improvement. However, these situations are rare.

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