See Also:

java.io.PrintStream.println()

java.io.PrintStream.println(boolean)

java.io.PrintStream.println(char)

java.io.PrintStream.println(char [])

java.io.PrintStream.println(double)

java.io.PrintStream.println(float)

java.io.PrintStream.println(int)

java.io.PrintStream.println(long)

java.io.PrintStream.println(java.lang.Object)

java.io.PrintStream.println(java.lang.String)

上面是println的所有方法,對(duì)于你傳遞的Course對(duì)象,println只能認(rèn)知為Object,然后我們來(lái)看

void java.io.PrintStream.println(Object x) 方法:

Prints an Object and then terminate the line. ?This method calls at first String.valueOf(x) to get the printed object's string value, then behaves as though it invokes print(String) and then ?println().

Parameters:

x ? The Object to be printed.

從上面可知,方法會(huì)首先調(diào)用一個(gè)String.valueOf(x)的方法講其變成一個(gè)字符串然后再輸出,x是你傳遞進(jìn)去的值.

所以你再自己去看String.valueOf(x)方法的內(nèi)容吧