英文:
If you pass an exception into Java's `System.out.println`, what happens?
问题
在Java中，我们通常将字符串作为输入传递给`System.out.println`函数。
如果您尝试输入一些奇怪的内容，例如`Exception`类的一个实例，会发生什么呢？
class Main {
public static void main(String[] args]) {
System.out.println("打印字符串是完全正常的");
Exception e = new Exception();
System.out.println(e);
}
}
哪些数据类型允许作为`System.out.println`的输入？
如果您尝试打印一个未为之重载的类的实例，会发生什么？
英文:
In java, we normally pass strings as input to System.out.println
What happens if you try to input something weird, such as an instance of the Exception class?
class Main {
public static void main(String[] args]) {
System.out.println("printing a string is perfectly normal");
Exception e = new Exception();
System.out.println(e);
}
}
What datatypes are allowed as input to System.out.println?
What happens if you attempt to print an instance of a class which System.out.println is not overloaded for?
答案1
得分: 0
这将调用带有Object参数的重载方法，其代码如下所示：
public void println(Object x) {
String s = String.valueOf(x);
synchronized (this) {
print(s);
newLine();
}
}
如果对象为null，这实际上会打印"null"，否则将打印调用对象的.toString方法的结果。
英文:
It calls the overloaded method with the Object parameter, which looks like this:
public void println(Object x) {
String s = String.valueOf(x);
synchronized (this) {
print(s);
newLine();
}
}
This essentially prints "null" if the object is null and will print the result of calling .toString on the object otherwise.
答案2
得分: 0
什么数据类型可以作为 System.out.println 的输入？
任何类型。
如果您尝试打印一个没有为其重载 System.out.println 的类的实例会发生什么？
有一个针对 Object 的重载，它的文档解释了发生的情况：对于参数 x，会调用 String.valueOf(x)，然后打印结果。
而如果您阅读该文档，它指出对于非空的 x，将调用 x.toString()。
简而言之，所有对象都有一个可访问的 toString() 方法，这决定了打印的内容。
英文:
> What datatypes are allowed as input to System.out.println?
Anything.
> What happens if you attempt to print an instance of a class which
> System.out.println is not overloaded for?
There is an overload for Object, and its documentation says what happens: for the argument x, a call to String.valueOf(x) is made, and the result is printed.
And if you read the documentation for that, it says that x.toString()will be called for non-nullx.
In short, all objects have an accessible toString() method, and that is what determines what is printed.
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