Wednesday, December 22, 2010

Java-Object Comparison


class ObjectComparison {
public static void main(String[] args) {
String s1 = new String("Hello");
String s2 = new String("Hello");

System.out.println("[Ref. Comparison]s1" +
((s1 == s2) ? " is " : " is not " ) +
"equal to s2.");/*(s1==s2) always return false since the references are compared here*/

System.out.println("[Value Comparison]s1" +
((s1.equals(s2)) ? " is " : " is not " ) +
"equal to s2.");/*(s1.equals(s2)) always return true since the values are compared here*/
}
}



---Overriding hashCode() in Rectangle---

public int hashCode() {
String hashStr = "L" + length + "B" + breadth;
return hashStr.hashCode();
}

-> class String has overridden the hashCode() in Object.
Implicitly created String object [String str = “hello”;] are stored in the string constant pool. Hence same valued String objects created implicitly have the same reference (and hence same hash code)- to impart optimization.
-> Implicit creation of object: String str = “hello”;
-> Explicit creation of object: String str = new String(“hello”);
-> class Rectangle makes use of hashCode() in the class String to mimic this behavior.
-> L and B are used as delimiters since Rectangle (11, 20) and Rectangle (1, 120) may have same hash code otherwise.

---Overriding hashCode() in Container---

public int hashCode() {
String hashStr = "L" + getLength() + "B" + getBreadth() + “H” + height;
return hashStr.hashCode();
}


---Overriding equals() in Rectangle---

public boolean equals(Object object) {
boolean equals = false;

if (object instanceof Rectangle &&
((Rectangle) object).getLength() == length &&
((Rectangle) object).getBreadth() == breadth) {
equals = true;
}

return equals;
}


---Overriding equals() in Container---

public boolean equals (Object object) {
boolean equals = false;

if (object instanceof Container &&
((Container) object).getLength() == getLength() &&
((Container) object).getBreadth() == getBreadth()&&
((Container) object).getHeight() == height) {
equals = true;
}

return equals;
}

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