java - Why do I get null pointer exception in this code? -

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public class test {      integer i;     int j;      public static void main ( string [] args ) {        test t = new test ();        t.go();     }      public void go() {        j=i;        system.out.println(j);        system.out.println(i);     } }

output : exception in thread "main" java.lang.nullpointerexception @ test.go(test.java:12) @ test.main(test.java:8)

that's not error. runtime nullpointerexception because you're unboxing null reference (i) primitive (j). see jls §5.1.8.

the reason i null instance fields initialized 0, null, or false default.


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