CareerCup

public int hashCode() {
int hash = 0;
for (int i = 0; i < length(); ++i) {
hash = 31 * hash + charAt(i);
}
return hash;
}

If two objects are equal as given by "equals()" then their hash codes should also be same, but if two objects have same hash code they don't necessarily need to be equal.

public class User {
	private String firstName;
	private String lastName;
	
	public boolean equals(Object obj){
		if(obj == null){return false;}
		if (obj instanceof User){
			User other = (User) obj;
			if(this.firstName.equals(other.firstName) && this.lastName.equals(other.lastName)){
				return true;
			}
		}
		return false;
	}
	public int hashCode(){
		return (firstName.hashCode() + lastName.hashCode());
	}
}

don't think if(obj == null){return false;} test is required.
If obj is null, instanceof operator returns false.

public class FullName {
private String firstname;
private String lastname;

@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result
+ ((firstname == null) ? 0 : firstname.hashCode());
result = prime * result
+ ((lastname == null) ? 0 : lastname.hashCode());
return result;
}
@Override
public boolean equals(Object obj) {
if (this == obj)
return true;
if (obj == null)
return false;
if (!(obj instanceof FullName)) {
return false;
}
final FullName other = (FullName) obj;
if (firstname == null) {
if (other.firstname != null)
return false;
} else if (!firstname.equals(other.firstname))
return false;
if (lastname == null) {
if (other.lastname != null)
return false;
} else if (!lastname.equals(other.lastname))
return false;
return true;
}
}

Better to not use instanceof when overriding equals method ( be careful for subclass)

We need to check and compare the classes of both the objects in equals()