Scanner input accepting Strings skipping every oth

问题:

This question already has an answer here:

How to use java.util.Scanner to correctly read user input from System.in and act on it? (1 answer)

Closed 4 years ago.

Alright, so the code is pretty straight forward. Generic class ourSet, that takes in some elements, puts it in a LinkedList, and does some functions on the two sets.

My problem is actually quite unrelated the general concept of the project, its more in the "user input interface" I've created. I want it to take in some Strings and add it to the set, then while receiving the string "EXIT" (all caps), to exit the loop, and do the same for the next set. What is happening is that the do while loop is only sending the 1st, 3rd, 5th,.. for all odd numbers.

package set.pkgclass;

import java.util.Scanner; 
import java.util.LinkedList; 


public class SetClass {


public static void main(String[] args) {

    ourSet<String> set1 = new ourSet<String>();  
    ourSet<String> set2 = new ourSet<String>(); 
    Scanner input = new Scanner(System.in); 



    System.out.println("Please enter a string to put in set 1, "
            + "type EXIT (in all caps) to end.");


    do {

        set1.add(input.nextLine());

    }
    while (!"EXIT".equals(input.nextLine()));


    System.out.println("Please enter a string to put in set 2, "
            + "type EXIT (in all caps) to end");

    do {

        set2.add(input.nextLine());
    }
    while (!"EXIT".equals(input.nextLine()));



    ourSet.intersection(set1,set2); 
    ourSet.difference(set1, set2);
    ourSet.union(set1, set2);








     }
  }

class ourSet<T>{




private LinkedList<T> mySet = new LinkedList<>();



public void add(T element){      
    mySet.add(element);
}

public void remove(T element){        
    mySet.remove(element);
}

public boolean membership(T element){        
    if(mySet.contains(element) == true) {
        return true; 
    }

    else {
    return false;
    }
}


public static <T> void union(ourSet<T> s1, ourSet<T> s2){
    System.out.print("The union is: ");
    for (int i=0; i < s1.mySet.size(); i++) {
        T t = s1.mySet.get(i);
        if (!s2.mySet.contains(t)){
            s2.add(t);
            }

    }

    for (int i=0; i < s2.mySet.size(); i++){
        T t = s2.mySet.get(i);
        System.out.print(t+", ");
    }
    System.out.println();  


}
public static <T> void intersection(ourSet<T> s1, ourSet<T> s2){ 
    System.out.print("The intersection is: ");
    for (int i=0; i < s1.mySet.size(); i++) {
        T t = s1.mySet.get(i); 
        if (s2.mySet.contains(t)) {
            System.out.print(t+", ");
        }
    }
    System.out.println();

}

public static <T> void difference(ourSet<T> s1, ourSet<T> s2){
    System.out.print("The difference is: ");
    for (int i=0; i < s1.mySet.size(); i++) {
        T t = s1.mySet.get(i);
        if (!s2.mySet.contains(t)) {
            System.out.print(t+", ");
        }

    }
    System.out.println();  
   }
 }

回答1:

The reason is, you're calling input.nextLine() twice:

do {

    set1.add(input.nextLine());

}
while (!"EXIT".equals(input.nextLine()));

A much easier way than do-while is while:

while (!(String in = input.nextLine()).equals("EXIT")) {
    set1.add(in);
}

回答2:

You ask for input twice

do {

    set1.add(input.nextLine()); // you enter a number

}
while (!"EXIT".equals(input.nextLine())); // what if you enter another number? 
// it'll just loop again, skipping that number

You need to ask for input once and use that either to stop or add it to your set.

回答3:

You loop is doing exactly what you've told it to...

• Read a line of text and add it to set1
• Read a line of text and check to see if it equals "EXIT"
• Repeat as required...

So, every second request is being used to check for the exit state. Instead, you should assign the text from the input to a variable and use it to do you checks, for example...

do {
    String text = input.nextLine();
    if (!"EXIT".equals(text)) {
        set1.add();
    }
} while (!"EXIT".equals(text));

ps- Yes, I know, you could use break ;)