String objects

[Vikram Nm]

String s1=new String("hi");
String s2=new String("hi");
System.out.println(s1.hashCode());
System.out.println(s2.hashCode());

This prints out the same hashcode on my machine
shouldn't it be different since they are different objects
and are not using the pool.

[Sandeep Nachane]

String Class overrides hashcode() method and looks at the contents of the string to determine the result of hashcode().
Sandeep Nachane

[Ajith Kallambella]

This is in compliance with the general contract of the hashCode method defined by the Object -

If two objects are equal according to the equals(Object) method, then calling the hashCode method on each of the two objects must produce the same integer result.

Since in your example s1.equals(s2) is true, s1.hashCode() must be equal to s2.hashCode().

FYI, the hashcode for a String object is computed as

s[0]*31^(n-1) + s[1]*31^(n-2) + ... + s[n-1]

using int arithmetic, where s[i] is the ith character of the string, n is the length of the string, and ^ indicates exponentiation. (The hash value of the empty string is zero )


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Ajith Kallambella M.
Sun Certified Programmer for the Java�2 Platform.
IBM Certified Developer - XML and Related Technologies, V1.