我认为 System.out.println()
和 System.err.println()
之间的区别只是消息打印到控制台的方式。含义 err
打印错误消息(红色),而 out
打印标准消息。我注意到它们与预期的不太相似(例如,错误消息将总是打印在输出消息之前)。
但是有一个例子让我特别困惑。假设我有这个简单的程序:
Scanner scanner = new Scanner(System.in);
while (true) {
int num = scanner.nextInt();
if (num > 0) {
System.out.println("All good, bye");
break;
} else {
System.out.println("Number must be possitive!");
System.out.print("New try:");
}
}
输出(来自我的测试):
但是当我制作字面上相同的代码并且只是更改消息“数字必须为正”以使用 System.err.println()
打印时:
Scanner scanner = new Scanner(System.in);
while (true) {
int num = scanner.nextInt();
if (num > 0) {
System.out.println("All good, bye");
break;
} else {
System.err.println("Number must be possitive!");
System.out.print("New try:");
}
}
输出(来自我的测试):
我不知道它是如何制作这些奇怪的印刷品的。有人能告诉我我错过了什么吗?
答案 0 :(得分:1)
我认为这是因为两个独立的流写入同一个控制台。
int i = 5;
while (--i>0) {
System.out.println("Number must be possitive!");
System.out.println("New try:");
}
System.out.println("\n\n with two separate streams \n");
i=5;
while (--i>0) {
System.err.println("Number must be possitive!");
System.out.println("New try:");
}
输出:
Number must be possitive!
New try:
Number must be possitive!
New try:
Number must be possitive!
New try:
Number must be possitive!
New try:
with two separate streams
Number must be possitive!
New try:
New try:
Number must be possitive!
Number must be possitive!
New try:
Number must be possitive!
New try:
由于两个流不同步,因此无法保证它们的写入顺序。
答案 1 :(得分:1)
我建议在控制台方面检查您的 IDE 设置。 它碰巧对我来说运行得很好:
我使用的代码基本相同:
import java.util.Scanner;
public class Main
{
public static void main(String[] args) {
System.out.print("Enter the number:");
Scanner scanner = new Scanner(System.in);
while (true) {
int num = scanner.nextInt();
if (num > 0) {
System.out.println("All good, bye");
break;
} else {
System.err.println("Number must be possitive!");
System.out.print("New try:");
}
}
}
}