char and int array difference

Question

When I try to print the uninitialized static char array it gives run time error (Null pointer exception) whereas the uninitialized static int array

Answer 1

System.out is an instance of PrintStream and this class has a few overloaded println methods. In your case:

1. System.out.println(ch); is using public void println(char x[])
2. System.out.println(arr); is using public void println(Object x) (there is no public void println(int[] x) method so the closest available type for int[] which println can use is Object).

The second method is using

String.valueOf(x);

to get a string representation of the object we want to print and the code of the valueOf method looks like

public static String valueOf(Object obj) {
    return (obj == null) ? "null" : obj.toString();
}

so it is null-safe (will return the string "null" if the reference holds null).

The first method is at some level using

public void write(char cbuf[]) throws IOException {
    write(cbuf, 0, cbuf.length);
                 //    ^^^^^^^ this throws NPE
}

and because cbuf is null cbuf.length will throw NullPointerException because null doesn't have length (or any other) field.