How to find a random entered number in a stack - stack

Question

So what I'm doing is creating a stack and then find a way to search for a random number in the stack. So basically if the code is:
Stack thisstack = new Stack();
Scanner userinput = new Scanner(System.in);
a = userinput.nextInt();
b = userinput.nextInt();
c = userinput.nextInt();
showpush(thisstack, a);
showpush(thisstack, b);
showpush(thisstack, c);
My question is how would i find a number the user inputs, and be able to throw an exception if we look for a number that isn't there. so if the stack the user inputs is [42, 543, 12] and we look for 42 it shows 42 but if we look for 43 it says something like "number not in stack"

Answer 1

Since Stack class inherits from Vector class, you have access to its contains() method.
contains() returns true if the object is in the stack; false if not, so one trivial implementation of the showpush() method would be:
void showpush(Stack stack, int num){
if (stack.contains(num)){
System.out.println(num);
} else {
System.out.println("number not in stack");
}
}
where num is your search target, and stack... well your stack.
One thing to note here is that when declaring a Stack (since it is a generic type) you also have to declare its type arguments (to ensure type safety), which bears the following change in thisstack's declaration:
Stack<Integer> thisstack = new Stack<Integer>();
You can also check Mureinik's answer here.
Edit/Appendix
Just for completeness, I have added a small demo with two different types of user input (int and float) being pushed into the stack. This is possible when declaring the stack with the more general <Object> type argument, as follows:
import java.util.Stack;
import java.util.Scanner;
public class Jst {
void showpush(Stack stack, Object obj){
if (stack.contains(obj)){
System.out.println("Found "+obj+" in stack");
} else {
System.out.println(obj+" not in stack");
}
}
public static void main(String[] Arguments){
Jst j = new Jst(); //either this way or declare showpush as static
Stack<Object> thisstack = new Stack<Object>();
Scanner userinput = new Scanner(System.in);
int a,pb;
float b,pa;
// get user input
System.out.print("Enter two numbers (int, float):");
try {
a = userinput.nextInt();
b = userinput.nextFloat();
} catch (Exception e) {
System.out.println("Exception : "+e.toString());
return;
}
// push user input into stack
System.out.print("\nPushing user input into stack...");
thisstack.push(a);
thisstack.push(b);
// check stack
System.out.println("Checking stack...");
j.showpush(thisstack, a);
j.showpush(thisstack, b);
// pop stack contents
System.out.print("\nPopping stack contents...");
pa = (float)thisstack.pop();
pb = (int)thisstack.pop();
System.out.println("Popped contents : [ "+pa+", "+pb+" ] (Notice that Stack is LIFO)");
// check stack
System.out.println("Checking stack...");
j.showpush(thisstack, a);
j.showpush(thisstack, b);
// push b back in stack
System.out.print("\nPushing "+b+" back into stack...");
thisstack.push(b);
// check stack
System.out.println("Checking stack...");
j.showpush(thisstack, a);
j.showpush(thisstack, b);
}
}
which yields:
C:\>java Jst
Enter two numbers (int, float):1 23.4
Pushing user input into stack...
Checking stack...
Found 1 in stack
Found 23.4 in stack
Popping stack contents...
Popped contents : [ 23.4, 1 ] (Notice that Stack is LIFO)
Checking stack...
1 not in stack
23.4 not in stack
Pushing 23.4 back into stack...
Checking stack...
1 not in stack
Found 23.4 in stack