returning an object

Given the code below which adds weight to an object
How can I create a method, NewTruckWeight() that will not change the state of the obj.
Instead I want it to add pounds using the state of the current obj, instantiating and returning a new truck obj, without altering the state of the current obj?

class TruckTest {
public static void main(String[] args){
Truck t1 = new Truck(5,125000);
Truck t2 = new Truck(6,17000);

//print the orginal weight of t1
System.out.println(t1.getWeight());

//call mutateWeight()
t1.mutateWeight(1000);
System.out.println(t1.getWeight());
System.out.println(t2.getWeight());

//here is the call NewTruckWeight(1000), I want to assign a new Truck reference to t2???

}
}

class Truck {
private int numaxles;
private int weight;

Truck(){
};
Truck(int axles, int w) {
numaxles = axles;
weight =w;
}
int getWeight() {
return weight;
}
int getnumaxles() {
return numaxles;
}

//add the mutateWeight()
int mutateWeight(int i) {
weight=(i + weight);
return weight;
}

//add NewTruckWeight()???{

}

}
Thanks, hope that is clear....

In excense, what you need is to clone the old object...
Their is an interface for this: Clone.

If you look into this interface, it should set you on the right track.