为什么print语句在java中调用**toString**方法?
问题描述：
为什么下面的代码段会自动调用toString()方法?
Why the following code segment auto calls toString() method?
public class Demo {
public Demo() {
System.out.println(this); // Why does this line automatically calls toString()?
}
public static void main(String[] args) {
Demo dm = new Demo();
}
}
答
println 针对各种类型重载，您调用的是:
println is overloaded for various types, the one you are invoking is:
java.io.PrintStream.println(java.lang.Object)
看起来像这样:
public void println(Object x) {
String s = String.valueOf(x);
synchronized (this) {
print(s);
newLine();
}
}
和 String.valueOf 看起来像这样:
public static String valueOf(Object obj) {
return (obj == null) ? "null" : obj.toString();
}
所以你可以看到它在你的对象上调用了 toString().QED
So you can see it calls toString() on your object. QED