Goto statements in Java [closed]

问题:

I executed the below code in Eclipse, but the GOTO statements in it are not effective. How do I use it?

How do I rewrite the above code using the Break and Continue statements without using the goto statement?

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 *
 */

/**
 * @author Home
 *
 */
public class student
{
    /**
    * @param args
    */
    String average(float sub1,float sub2,float sub3)
    {
        float average = (sub1+sub2+sub3)/3;
        if( average > 50)
            return "PASS";
        else
            return "FAIL";
    }

    String addName(String name)
    {
        return name;
    }

    public static void main(String[] args) throws NumberFormatException, IOException
    {
        // TODO Auto-generated method stub
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        student stu = new student();
        int loop_option = 0;
        do
        {
            System.out.println("--------------STUDENT DETAILS---------------");
            System.out.println("Choose the operation from the following options.");
            System.out.println(" 1.ADDNAME");
            System.out.println(" 2.AVERAGE_RESULT");
            System.out.println(" 3.EXIT");
            System.out.println("CHOOSE THE OPERATION U WANT:");

            int option = Integer.parseInt(br.readLine());
            switch(option)
            {
                case 1:
                    System.out.println("Enter the name");
                    String name = br.readLine();
                    System.out.println("The Inserted student name is " +stu.addName(name));
                break;

                case 2:
                    outsideloops:
                    System.out.println("Enter the marks (in 100):");
                    System.out.println("Subject 1:");
                    float sub1 = Float.parseFloat(br.readLine());
                    if (sub1 >= 101)
                        goto outsideloops;
                    System.out.println("Subject 2:");
                    float sub2=Float.parseFloat(br.readLine());
                    System.out.println("Subject 3:");
                    float sub3=Float.parseFloat(br.readLine());
                    System.out.println("The Student is "+stu.average(sub1,sub2,sub3)+ "in the examinations");
                    break;

                case 3:
                    System.exit(0);

                default:
                    System.out.println("Please choose the valid option");
                    //break;
            }
            System.out.println("if U want 2 use further press 1 to continue...");
           loop_option=Integer.parseInt(br.readLine());
        }
        while (loop_option == 1);
        System.out.println("The STUDENT program is terminating now.");
    }
}

By the following code as suggested by one of the Stack Overflow members made me to write the following code:BUT that is also wrong.. I am thinking why the deleted the GOTO statements in Java?

This is not working either.

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    String average(float sub1,float sub2,float sub3)
    {
        float average=(sub1+sub2+sub3)/3;
        if( average>50)
            return "PASS";
        else
            return "FAIL";
    }

    String addName(String name)
    {
        return name;
    }

    public static void main(String[] args) throws NumberFormatException, IOException {
        // TODO Auto-generated method stub
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        Main stu = new Main();

        float sub1 = 0;
        int goThere = 0;

        do {
            switch(goThere){
                case -1:
                    System.out.println("if U want 2 use further press 0 to continue...");
                    goThere = Integer.parseInt(br.readLine());
                    continue;

                case 0:
                    System.out.println("--------------STUDENT DETAILS---------------");
                    System.out.println("Choose the operation from the following options.");
                    System.out.println(" 1.ADDNAME");
                    System.out.println(" 2.AVERAGE_RESULT");
                    System.out.println(" 3.EXIT");
                    System.out.println("CHOOSE THE OPERATION U WANT:");

                    goThere = Integer.parseInt( br.readLine() );
                    continue;

                case 1:
                    System.out.println("Enter the name");
                    String name = br.readLine();
                    System.out.println("The Inserted student name is " + stu.addName(name));
                    goThere = -1;
                    continue;

                case 2:
                    System.out.println("Enter the marks (in 100):");
                    System.out.println("Subject 1:");
                    sub1 = Float.parseFloat(br.readLine());
                    goThere = 4;
                    continue;

                case 4:
                    {
                        if( sub1 >= 101)
                        {
                            goThere = 2;
                        }
                        else {goThere = 3;}
                    }
                    continue;

                case 3:
                    System.out.println("Subject 2:");
                    float sub2=Float.parseFloat(br.readLine());
                    goThere =5;
                    continue;

                case 5:
                    {
                        if( sub2 >= 101)
                        {
                            goThere = 3;
                        }
                        else {
                            goThere = 6;
                        }
                    }
                    continue;

                case 6:
                    System.out.println("Subject 3:");
                    float sub3 = Float.parseFloat(br.readLine());
                    goThere = 7;
                    continue;

                case 7:
                    {
                        if( sub3 >= 101)
                        {
                            goThere = 6;
                        }

                    }
                    continue;

                    System.out .println("The Student is " + stu.average(sub1,sub2,sub3) + "in the examinations");
                    goThere = -1;
                    continue;
            }
            break;
        } while(true);
    }
}

回答1:

There is no goto in Java as of yet. It's a reserved word, in case there ends up being the need for it, but as far as I know, they haven't used it yet.

Probable equivalent code:

case 2:
    float sub1 = 0.0;
    do {
        System.out.println("Enter the marks (in 100):");
        System.out.println("Subject 1:");
        sub1 = Float.parseFloat(br.readLne());
    } while (sub1 >= 101);

    ... rest of the code ...

Note, this code would be equivalent for this particular situation. There's no universal replacement for goto; if there were, they'd just call it goto and be done with it. Each case will be different, and the replacement will depend entirely on how the goto would have been used.

回答2:

You don't have to use goto (already there isn't) Ok. Let's think for this problem. I think this is may be useful

public class Goto
{

    public static void main(String[] args)
    {
        int goThere = 0;

        do
        {
            switch(goThere)
            {
                case 0:
                case 1:
                    System.out.println("Foo");
                    goThere = 3;
                    continue;

                case 2:
                    System.out.println("Baz");
                    goThere = -1;
                    continue;
                case 3:
                    System.out.println("Bar");
                    goThere = 2;
                    continue;
             }
        } while(false);
    }
}

Try this. And may be you can extend that code.

回答3:

According to this:

In Java, goto is a reserved word, but is unusable.

回答4:

As others pointed, there is no goto statement in Java. I want to add that labels are a slight alternative.

回答5:

Jumping forward

label: if (true) {
    // Do stuff
    if (check)
        break label;
    // Do more stuff
}

Jumping backward

label: do {
    // Do stuff
    if (check)
        continue label;
    // Do more stuff
    break;
} while(true);

It is not to be used in any sensible piece of software ;-)

回答6:

While goto is a reserved keyword in Java, there is no goto statement.

回答7:

Rewrite for your code is here,

Put your "Student" class in the same package then Main.java;

package MyPackage

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class Main {
    public static void main(String[] args) throws NumberFormatException, IOException {
        // TODO Auto-generated method stub
        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        Student stu = new Student();

        float sub1 = 0;
        int goThere = 0;

        do {
            switch(goThere){
                case -1:
                    System.out.println("if U want 2 use further press 0 to continue...");
                    goThere = Integer.parseInt(br.readLine());
                continue;

                case 0:
                    System.out.println("--------------STUDENT DETAILS---------------");
                    System.out.println("Choose the operation from the following options.");
                    System.out.println(" 1.ADDNAME");
                    System.out.println(" 2.AVERAGE_RESULT");
                    System.out.println(" 3.EXIT");
                    System.out.println("CHOOSE THE OPERATION U WANT:");

                    goThere = Integer.parseInt( br.readLine() );
                continue;

                case 1:
                    System.out.println("Enter the name");
                    String name = br.readLine();
                    System.out.println("The Inserted student name is " + stu.addName(name));
                    goThere = -1;
                continue;

                case 2:
                    System.out.println("Enter the marks (in 100):");
                    System.out.println("Subject 1:");
                    sub1 = Float.parseFloat(br.readLine());
                    goThere = 4;
                continue;

                case 4:
                    if( sub1 >= 101){
                        goThere = 2;
                        continue;
                    }

                    System.out.println("Subject 2:");
                    float sub2=Float.parseFloat(br.readLine());
                    System.out.println("Subject 3:");
                    float sub3=Float.parseFloat(br.readLine());
                    System.out.println("The Student is " + stu.average(sub1,sub2,sub3) + "in the examinations");
                    goThere = -1;
                continue;
             }
            break;
        } while(true);
    }
}