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    <p><strong>Strings in Java are immutable</strong>. Basically this means that, once you create a string object, you won't be able to modify/change the content of a string. As a result, if you perform any manipulation on a string object which "appears to" change the content of the string, Java creates a new string object, and performs the manipulation on the newly created one.</p> <p>Based on this, your code above appears to create five string objects - two are created by the declaration, two are created by calls to <code>substring</code>, and the last one is created after you concatenate the two pieces.</p> <p>Immutability however leads to another interesting consequence. JVM internally maintains something like a string pool for creating string literals. For saving up memory, JVM will try to use string objects from this pool. Whenever you create a new string literal, JVM will loop into the pool to see if any existing strings can be used. If there is, JVM will simply use it and return it.</p> <p>So, technically, before Java 7, JVM will create only one string object for your whole code. Even your <code>substring</code> calls won't create new string objects in the pool, it will use the existing "Hello World" one, but in this case it will only use characters from position 0 to 3 for your first call to substring, for example. Starting from Java 7, substring will not share the characters, but will create a new one. So, total object count will be 4 - the last one will be created with the concatenation of the two substrings.</p> <p><strong>Edit</strong> To answer your question in the comment, take a look at <a href="http://docs.oracle.com/javase/specs/jls/se7/html/jls-10.html#jls-10.9" rel="nofollow">Java Language Specification</a> - </p> <blockquote> <p>In the Java programming language, unlike C, an array of char is not a String, and neither a String nor an array of char is terminated by '\u0000' (the NUL character).</p> <p>A String object is immutable, that is, its contents never change, while an array of char has mutable elements.</p> <p>The method toCharArray in class String returns an array of characters containing the same character sequence as a String. The class StringBuffer implements useful methods on mutable arrays of characters.</p> </blockquote> <p>So, no, char arrays are not immutable in Java, they are mutable.</p>
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    1. USMD Sayem Ahmed
    1. USMD Sayem Ahmed
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    1. COTechnically, only 4 are created. String literals in code are resolved with `String.intern()`, so a and b both refer to the exact same String at runtime.
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    2. COThanks for the great answer.
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    3. CO"two are created by the declaration"?
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      1. USZiyao Wei
 

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