How to use goto statement correctly

Question

I am taking my high school AP Computer Science class    I decided to throw a goto statement into a one of our labs just to play around  but I got this error    Exception in thread  main  java lang Error  Unresolved compilation problems       Syntax error on token  goto   assert expected     restart cannot be resolved to a variable at Chapter 3 Lab03 Chapter3 Factorial main Factorial java 28    I went to a goto question on Stackoverflow to find out how to do it properly  and I did exactly as was demonstrated in one of the answers  I really don t understand why the compiler wants an assert statement  at least that s what I assume it wants   nor do I have any idea how to use assert  It seems to want the restart part of goto restart  to be a variable  but restart is just a label that pulls the program back up to line 10 so that the user can enter a valid int  If it wants restart to be a variable  how do I do that   import java util     public class Factorial        public static void main String   args                 int x   1          int factValue   1          Scanner userInput   new Scanner System in           restart          System out println  Please enter a nonzero  nonnegative value to be factorialized             int factInput   userInput nextInt             while factInput lt  0                        System out println  Enter a nonzero  nonnegative value to be factorialized                 factInput   userInput nextInt                       if x lt 1   This is another way of doing what the above while loop does  I just wanted to have some fun                        System out println  The number you entered is not valid  Please try again                 goto restart                    while x lt  factInput                        factValue  x              x                      System out println factInput        factValue           userInput close

User · Answer

If you look up continue and break they accept a "Label". Experiment with that. Goto itself won't work.

public class BreakContinueWithLabel {

    public static void main(String args[]) {

        int[] numbers= new int[]{100,18,21,30};

        //Outer loop checks if number is multiple of 2
        OUTER:  //outer label
        for(int i = 0; i<numbers.length; i++){
            if(i % 2 == 0){
                System.out.println("Odd number: " + i +
                                   ", continue from OUTER label");
                continue OUTER;
            }

            INNER:
            for(int j = 0; j<numbers.length; j++){
                System.out.println("Even number: " + i +
                                   ", break  from INNER label");
                break INNER;
            }
        }      
    }
}

User · Answer

goto doesn t do anything in Java

User · Answer

As already pointed out by all the answers goto - a reserved word in Java and is not used in the language   restart  is called an identifier followed by a colon   Here are a few things you need to take care of if you wish to achieve similar behavior -   outer                      Should be placed exactly before the loop loopingConstructOne        We can have statements before the outer but not inbetween the label and the loop               inner      loopingConstructTwo           continue           This goes to the top of loopingConstructTwo and continue          break              This breaks out of loopingConstructTwo          continue outer     This goes to the outer label and reenters loopingConstructOne          break outer        This breaks out of the loopingConstructOne          continue inner     This will behave similar to continue          break inner        This will behave similar to break            I m not sure of whether should I say similar as I already have

User · Answer

There is not  goto  in the Java world  The main reason was developers realized that complex codes which had goto would lead to making the code really pathetic and it would be almost impossible to enhance or maintain the code    However this code could be modified a little and using the concept of continue and break we could make the code work       import java util     public class Factorial        public static void main String   args                 int x   1          int factValue   1          Scanner userInput   new Scanner System in           restart  while true           System out println  Please enter a nonzero  nonnegative value to be factorialized             int factInput   userInput nextInt             while factInput lt  0                        System out println  Enter a nonzero  nonnegative value to be factorialized                 factInput   userInput nextInt                       if x lt 1   This is another way of doing what the above while loop does  I just wanted to have some fun                        System out println  The number you entered is not valid  Please try again                 continue restart                    while x lt  factInput                        factValue  x              x                      System out println factInput        factValue           userInput close            break restart

User · Answer

goto is an unused reserved word in the language  So there is no goto  But  if you want absurdist theater you could coax one out of a language feature of labeling  But  rather than label a for loop which is sometimes useful you label a code block  You can  within that code block  call break on the label  spitting you to the end of the code block which is basically a goto  that only jumps forward in code       System out println  1        System out println  2        System out println  3        my goto                System out println  4            System out println  5            if  true  break my goto          System out println  6            goto end location      System out println  7        System out println  8      This will print 1  2  3  4  5  7  8  As the breaking the code block jumped to just after the code block  You can move the my goto    and if  true  break my goto  and     goto end location  statements  The important thing is just the break must be within the labeled code block   This is even uglier than a real goto  Never actually do this   But  it is sometimes useful to use labels and break and it is actually useful to know that if you label the code block and not the loop when you break you jump forward  So if you break the code block from within the loop  you not only abort the loop but you jump over the code between the end of the loop and the codeblock

User · Answer

The Java keyword list specifies the goto keyword  but it is marked as  not used    This was probably done in case it were to be added to a later version of Java   If goto weren t on the list  and it were added to the language later on  existing code that used the word goto as an identifier  variable name  method name  etcetera  would break  But because goto is a keyword  such code will not even compile in the present  and it remains possible to make it actually do something later on  without breaking existing code

User · Answer

Java does not support goto  it is reserved as a keyword in case they wanted to add it to a later version

User · Answer

Java also does not use line numbers  which is a necessity for a GOTO function  Unlike C C    Java does not have goto statement  but java supports label  The only place where a label is useful in Java is right before nested loop statements  We can specify label name with break to break out a specific outer loop

[java] How to use goto statement correctly

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