Exception in thread "main" java.lang.NumberFormatException: For input string: "t1"?

Question

I'm new to Java and I've got this problem here. I'll post the link and keep in mind, that the other similar questions here couldn't helped me since I have a different code, and because of that I made this account here.

Code:

package secret.package.guys;

import java.util.Scanner;

public class NewClass {
public static void main(String[] args) {

    System.out.println("Number: ");
    Scanner scanner = new Scanner(System.in); 
    String data=scanner.nextLine(); 
    System.out.println(data);


    int a = 0; 

    while(a < 6) {
        System.out.println(a);
        a++; 
        }

    if (a > 6){ 
        System.out.println("SAFE SPACE");


    } else {
        System.out.println("Get in the Safe Space");
        System.out.println("PERSON has entered the Safe Space. Safe Space closes instantly.");
    }                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                 
    String s = new String("Old marks: ");
    String t = new String("5.5"); 
    String u = new String("4"); 
    String v = new String("3"); 
    String w = new String("2.5"); 
    String x = new String("6.0"); 
    String y = new String("5.2"); 
    String z = new String("4"); 

    String t1 = t.replaceAll("5.5", "6");
    String u1 = u.replaceAll("4", "4");
    String v1 = v.replaceAll("3", "5");
    String w1 = w.replaceAll("2.5", "3");
    String x1 = x.replaceAll("6.0", "2");
    String y1 = y.replaceAll("5.2", "1.8");
    String z1 = z.replaceAll("4", "4.4");
    System.out.println("New: " + s + " " + t1 + " " + u1 + " " + v1 + " " + w1 + " " 
    + x1 + " " + y1 + " " + z1);
    System.out.println("Enter new marks: ");

    int foo = Integer.parseInt("t1"); 
    int foo1 = Integer.parseInt("u1"); 
    int foo2 = Integer.parseInt("v1"); 
    int foo3 = Integer.parseInt("w1"); 
    int foo4 = Integer.parseInt("x1"); 
    int foo5 = Integer.parseInt("y1"); 
    int foo6 = Integer.parseInt("z1"); 

    System.out.println("foo1 + foo2 + foo3 + foo4 + foo5 + foo6");

}   

}

Answer 1

You have to call parseInt on the value of the String variable, not on the variable name.

For example,

int foo = Integer.parseInt("t1"); 

should be

int foo = Integer.parseInt(t1); 

And that would only work if t1 contains a String representation of an integer (this means parseInt(z1) and parseInt(y1) would still fail since those Strings don't contain integers).

Answer 2

Your code tries to parse a String into a numerical value.

With the value "1" it would work, but since "t1" is not a valid numerical value, it will fail, and result in this Exception.

What I assume you want is, instead of:

int foo = Integer.parseInt("t1"); 

where you pass "t1" as a String

int foo = Integer.parseInt(t1); 

with the reference variable t1.