Java String vs String Buffer

Question

I have the following lines from the Java code

{        
         String str1=new String("Vivek");
         String str2=new String("Vivek");
         StringBuffer str3=new StringBuffer("Vivek");
         StringBuffer str4=new StringBuffer("Vivek");
         System.out.println(str1.equals(str2));
         System.out.println(str3.equals(str4));
}

Now i get the output as following

    True
    False

I cant get why it prints true for String oject and false for objects of StringBuffer? Has it to do something with mutability of objects?

You're a magician! This cannot compile. Did you meant `StringBuffer str3=new StringBuffer("Vivek");`? — Alexis C., May 08 '14 at 14:20
The `StringBuffer` class does simply not override equals. Since you create two brand new instances, it returns false. — Alexis C., May 08 '14 at 14:22
`StringBuffer` does not override the `equals` method from `Object`. — Omoro, May 08 '14 at 14:23
`str3.equals(str4)` is equivalent to `object.equals(object)` — Braj, May 08 '14 at 14:23
Unrelated note: if you don't need the thread-safty of StringBuffer, use StringBuilder. — Puce, May 08 '14 at 14:27

Reimeus · Answer 1 · 2014-05-08T14:58:26.247

4

StringBuffer does not override equals so calls the method of the superclass Object. If you want to compare content use the toString method

System.out.println(str3.toString().equals(str4.toString()));

Note Since Java 1.5 StringBuffer has been superceded by StringBuilder as a non-threaded alternative

edited May 08 '14 at 14:58

answered May 08 '14 at 14:23

Reimeus

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3

In other words, they weren't designed to be compared. – biziclop May 08 '14 at 14:23

score 1 · Answer 2 · answered May 08 '14 at 14:24

Because the equals in class String has been over-written to compare the content while the equals in class StringBuffer remained inherited from class Object which compares the address.

See there javadoc for both and you will understand more.

In String.equals:

Compares this string to the specified object. The result is true if and only if the argument is not null and is a String object that represents the same sequence of characters as this object.

Overrides: equals(...) in Object
Parameters:
anObject The object to compare this String against
Returns:
true if the given object represents a String equivalent to this string, false otherwise
See Also:
compareTo(String)
equalsIgnoreCase(String)

You may use:

str3.toString().equals(str4);

Yup...got it now...so the point is that String class overrides the equlas methods from the Object class and StringBuffer does not... — Vivek Patil Linksys3966, May 08 '14 at 16:40

Java String vs String Buffer

2 Answers2