Jumping to lines in Java

Question

I have just now started learning Java and one of the differences I noticed from C++ and VB is that Java has no goto statements, which I tend to use a lot while programming.

Is there any way I could jump between lines using another statement? I tried to use break and continue but to no avail (I might be doing something wrong).

Here is the code with goto statements and how I want it to operate:

public class HelloWorld {

static Scanner sc = new Scanner(System.in);
public static void main(String[] args)
{
    jump1:
    System.out.print("What do you want to calculate? ");
    String method = sc.nextLine();
    if (method.equals("tax")) tax();
    else {
        System.out.print("Please input a valid method. \n\n");
        goto jump1;
    }  
}

What is a good replacement for the goto commands?

Answer 1

You should avoid "goto" statements in all languages, according to the rules of "structured programming", instead using if-then-else or do or while or for loops to control program flow.

Java DOES have a sort of "goto" statement that you COULD use to only slightly modify your code, but consider the while loop below and the break statement, which jumps out of the loop.

  public static void main(String[] args) {
    String method = "";
    while(! method.equals("tax")){
      System.out.print("What do you want to calculate? ");
      method = sc.nextLine();
      if(method.equals("tax"))
        break;
      System.out.print("Please input a valid method. \n\n");
    }
    tax();
  }

The break statement enables your "Please ... valid" statement to display. You could also use this:

  public static void main(String[] args) {
    String method = "";
    while(! method.equals("tax")){
      System.out.print("What do you want to calculate? ");
      method = sc.nextLine();
    }
    tax();
  }

I also kind of like this:

  public static void main(String[] args) {
    String method = "";
    while(1==1){
      System.out.print("What do you want to calculate? ");
      method = sc.nextLine();
      if(method.equals("tax")
        break;
      System.out.print("Please input a valid method. \n\n");
    }
    tax();
  }

You might go to the Java tutorials; they're good.

Answer 2

A while loop in this instance.

http://docs.oracle.com/javase/tutorial/java/nutsandbolts/flow.html

For this (very specific) instance you could put

System.out.print("What do you want to calculate? ");

String method = sc.nextLine();
while (!method.equals("tax"))
{
    System.out.print("Please input a valid method. \n\n");
    method = sc.nextLine();
}
tax();

Obviously this only works if your only expected correct input is "tax", but it's a structure to build on.

Answer 3

You would want to put your if-statement in a while-loop by using the hasNextLine() function, which will loop until theres no more lines left to iterate over:

while(sc.hasNextLine()) {
    // Your code..
}

For more info regarding the function check Scanner::hasNextLine documentation.

Answer 4

In this case you can use a do-while-loop, which will do the statement first and will only repeat if the statement is true:

public class HelloWorld {

static Scanner sc = new Scanner(System.in);
public static void main(String[] args)
{
  boolean right = true;

    do {
      if(right)
        System.out.print("What do you want to calculate? ");
      else
        System.out.print("Please input a valid method. \n\n");

      String method = sc.nextLine();
      boolean right = false;
    } while (!method.equals("tax"));
    tax();

    }  
}