Question

一道java选择题

import javax.swing.*;public class ShowErrors
{public static void main(String[] args)
{int i;int j;
String s = JOptionPane.showInputDialog(null, "Enter an integer", "Input", JOptionPane.QUESTION_MESSAGE);
j = Integer.parseInt(s);
i = (i + 4);
}
}
1、  The program cannot compile because j is not initialized.
2、  The program cannot compile because i does not have an initial value when it is used in i = i + 4;
3、  The program compiles but has a runtime error because i does not have an initial value when it is used in i = i + 4;
4、  The program compiles and runs fine.

答案选2，但是int不是默认i=0吗？为什么2选项还说i没初始化呢

Answer 1

类的成元变量才有默认的缺省值，成员函数中的变量则必须赋初值。

Answer 2

int的全局变量，会初始化默认为0；
方法内的成员变量需要赋初值，否则不仅不能运行，就连编译都不会通过。

Answer 3

作为一个局部变量，它必须被显示的初始化，否则不能使用……

Answer 4

大家都说了 我也就不说了