提问人：Allen 提问时间：7/23/2023 更新时间：7/27/2023 访问量：55
break 语句在 java 中不会立即停止执行 while 循环
break statement does not stop executing while loop Immediately in java
问：
我正在尝试运行一个程序，要求用户列出一些值。然后，这些值将存储在一个列表中，一旦用户键入 0，循环就应该终止，程序应该找到用户输入的最小和最大值。
我初始化循环以存储值的代码如下：
public static void main(String[] Args){
Scanner in = new Scanner(System.in);
ArrayList<Integer> list = new ArrayList<>();
System.out.println("This program finds the largest and smallest numbers");
while(true) {
System.out.println("?");
int value = in.nextInt();
if(value == 0) {break;}
list.add(value);
}
System.out.println("smallest:" + findSmallest(list));
System.out.println("largest:" + findLargest(list));
}
break 语句不会在将输入 0 添加到列表之前立即退出 while 循环，而是在整个 while 循环完成后触发。例如，如果我输入 5,3 和 0，我应该得到：
最小：3 最大：5
但相反，我得到：
最小：0 最大：5
为什么会发生这种情况，我该如何解决？
作为参考，以下是整个代码：
package Programs;
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class FindRange {
/* sentinel value for exiting the program*/
private static final int sentinel = 0;
public static void main(String[] Args){
Scanner in = new Scanner(System.in);
ArrayList<Integer> list = new ArrayList<>();
System.out.println("This program finds the largest and smallest numbers");
while(true) {
System.out.println("?");
int value = in.nextInt();
if(value == 0) {break;}
list.add(value);
}
System.out.println("smallest:" + findSmallest(list));
System.out.println("largest:" + findLargest(list));
}
/*
* Precondition: We must receive a list of type ArrayList containing
* int values provided by the user
* PostConditions: Provides the smallest value in the list
* */
private static int findSmallest(ArrayList<Integer> list){
int smallest = list.get(0);
for (int i=0;i<list.size()-1;i++) {
if (i<smallest) {
smallest = i;
}
}
return smallest;
}
/*
* Precondition: We must receive a list of type ArrayList containing
* int values provided by the user
* PostConditions: Provides the Largest value in the list
*
* Error with code: Some reason break statement on main doesn't stop the execution of the loop straight away
* resulting in the sentinel 0 being stored in the list.
* */
private static int findLargest(ArrayList<Integer> list){
int Largest = list.get(0);
for (int i=0;i<list.size()-1;i++) {
if (i>Largest) {
Largest = i;
}
}
return Largest;
}
}
答：
1赞
Slaw
#1
您的工作正常。问题出在 和 的实现中。例如，您有：breakfindSmallestfindLargest
private static int findSmallest(ArrayList<Integer> list){
int smallest = list.get(0);
for (int i=0;i<list.size()-1;i++) {
if (i<smallest) {
smallest = i;
}
}
return smallest;
}
这里是索引，而不是该索引的值。此外，您的循环条件是错误的。它已经是排他性的，因为您正在使用 ，这意味着您不应该从列表的大小中减去一个。i<
你想要这样的东西：
private static int findSmallest(ArrayList<Integer> list){
int smallest = list.get(0);
for (int i = 0; i < list.size(); i++) {
if (list.get(i) < smallest) {
smallest = list.get(i);
}
}
return smallest;
}
或者，您可以使用 for-each 循环：
private static int findSmallest(ArrayList<Integer> list){
int smallest = list.get(0);
for (Integer value : list) {
if (value < smallest) {
smallest = value;
}
}
return smallest;
}
需要对 进行类似的更改。findLargest
1赞
tans flou
7/23/2023
#2
实际上，您不会将列表中的项目与最小变量和最大变量进行比较。您只需将 for 循环的索引与它们进行比较，因此您需要按如下方式更改它们：
private static int findSmallest(ArrayList<Integer> list) {
int smallest = list.get(0);
for (int i = 0; i < list.size(); i++) {
if (list.get(i) < smallest) {
smallest = list.get(i);
}
}
return smallest;
}
private static int findLargest(ArrayList<Integer> list) {
int Largest = list.get(0);
for (int i = 0; i < list.size(); i++) {
if (list.get(i) > Largest) {
Largest = list.get(i);
}
}
return Largest;
}
0赞
Oleg Cherednik
7/23/2023
#3
实际上，您不需要保留数组。您只需要两个值。int
public static void main(String... args) {
Scanner scan = new Scanner(System.in);
System.out.println("This program finds the largest and smallest numbers.");
System.out.println("Type '0' to exit the program.");
int min = Integer.MAX_VALUE;
int max = Integer.MIN_VALUE;
boolean empty = true;
while (true) {
System.out.print("> ");
int val = scan.nextInt();
if (val == 0) {
break;
}
min = Math.min(min, val);
max = Math.max(max, val);
empty = false;
}
if (empty) {
System.out.println("No input");
} else {
System.out.println("smallest: " + min);
System.out.println("largest: " + max);
}
}
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