求指导这个异常怎么解决
package myFirst;
public class TestBox {
Integer i;
int j;
public static void main(String[] args) {
TestBox t = new TestBox();
t.go();
}
public void go() {
j = i;
System.out.println(j);
System.out.println(i);
}
}
抛出异常如下:
Exception in thread "main" java.lang.NullPointerException
at myFirst.TestBox.go(TestBox.java:11)
at myFirst.TestBox.main(TestBox.java:8)