[英]How to use do-while loop to check user input again?
我想在程序中添加一个循环,以便当用户输入错误的名称时,它可以返回到程序的开头,并要求他们再次输入其名称。 我认为我需要一个do-while
循环,但是我不确定如何使用if语句和已经包含的布尔值来实现它。 我希望用户只有三个条目,如果他们输入了3次错误,则程序将关闭。
import java.util.Scanner;
public class Username
{
public static void main(String[] args)
{
{
Scanner kb = new Scanner(System.in);
// array containing usernames
String[] name = {"barry", "matty", "olly", "joey"}; // elements in array
System.out.println("Enter your name");
String name1 = kb.nextLine();
boolean b = true;
for (int i = 0; i < name.length; i++)
{
if (name[i].equals(name1))
{
System.out.println("you are verified you may use the lift");
b = false;
break;// to stop loop checking names
}
}
if (b)
{
System.out.println("Invalid entry 2 attempts remaining, try again");
}
}
您可以在while循环中使用条件。 类似于以下内容:
boolean b = false;
while(!b){
System.out.println("Enter your name");
String name1 = kb.nextLine();
for (int i = 0; i < name.length; i++) {
if (name[i].equals(name1)) {
b = true;
System.out.println("you are verified you may use the lift");
}else{
System.out.println("Invalid entry 2 attempts remaining, try again");
}
}
}
如果满足名称条件,则循环将退出,否则将循环。
您可以这样做:
int count = 0;
point:
do {
System.out.println("Enter your name");
String name1 = kb.nextLine();
boolean b = true;
for (int i = 0; i < name.length; i++) {
if (name[i].equals(name1)) {
System.out.println("you are verified you may use the lift");
b = false;
break point;// to stop loop checking names
}
}
if (b) {
count++;
System.out.println("Invalid entry 2 attempts remaining, try again");
}
while(!b || count <=3)
package com.loknath.lab;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Scanner;
public class User1 {
public static void main(String[] args) {
Scanner kb = new Scanner(System.in);
// array containing usernames
String[] name = {"zerr", "barry", "matty", "olly", "joey" }; // elements
String []temp=name;
Arrays.sort(temp);
while (true) {
System.out.println("Enter your name");
String name1 = kb.nextLine();
if (Arrays.binarySearch(temp,name1)>=0) {
System.out.println("you are verified you may use the lift");
break;
} else {
System.out.println("Not a verified user try again!");
}
}
System.out.println("Done");
}
}
产量
Enter your name
loknath
Not a verified user try again!
Enter your name
chiku
Not a verified user try again!
Enter your name
zerr
you are verified you may use the lift
Done
使用以下方法。 好在,这是一个干净而强大的解决方案。
import java.util.Arrays;
import java.util.List;
import java.util.Scanner;
public class AccessPoint
{
private Scanner scanner;
private List<String> usernames;
public AccessPoint()
{
scanner = new Scanner(System.in);
usernames = Arrays.asList("Barry", "Matty", "Olly", "Joey");
if (tryAccessForTimes(3))
{
allowAccess();
}
else
{
denyAccess();
}
scanner.close();
}
public static void main(String[] args)
{
new AccessPoint();
}
private boolean tryAccessForTimes(int times)
{
boolean accessAllowed = false;
for (int tryIndex = 1; tryIndex <= times && !accessAllowed; tryIndex++)
{
String userInput = getUserName();
for (String userName : usernames)
{
if (userName.equals(userInput))
{
accessAllowed = true;
break;
}
}
if (!accessAllowed)
{
printNumberOfTriesLeft(times, tryIndex);
}
}
return accessAllowed;
}
private void printNumberOfTriesLeft(int times, int tryIndex)
{
int triesLeft = times - tryIndex;
if (triesLeft != 0)
{
System.out.println("You have " + triesLeft
+ (triesLeft == 1 ? " try" : " tries") + " left.");
}
}
private String getUserName()
{
System.out.print("Enter Username: ");
return scanner.nextLine();
}
private void allowAccess()
{
System.out.println("Access Granted. Allowed to use lift.");
}
private void denyAccess()
{
System.out.println("Access Denied.");
}
}
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