jtips exam2.No.28-Exception

[jordan gong]

Can anyone help me? I could not understand why the output is 4.
The third try is not reached?
28.Given
class Test {
static String s="Java";
boolean b;
Test() {
super();
}
Test(String x) {
x=null;
try {
if ( b=(s.length() == 4) && (x.length() == 4))
System.out.println(b);
}
catch(java.lang.NullPointerException e) {
System.out.println("Exception 1 caught");
}

try {
if ( b=(s.length() == 4) | | (x.length() == 4))
System.out.println(b);
}
catch(java.lang.NullPointerException e) {
System.out.println("Exception 2 caught");
}
try {
if ( b=(s.length() != 4) && (x.length() == 4))
System.out.println(b);
}
catch(java.lang.NullPointerException e) {
System.out.println("Exception 3 caught");
}
}
public static void main(String [] args) {
Test t = new Test(s);
}
}
What is the output?
1.Prints
Exception 1 caught
true
true
2.Prints
Exception 1 caught
true
false
3.Prints
true
true
Exception 3 caught
4.Prints
Exception 1 caught
true

5.compile-time error occurs.
6.Run time Exception is thrown.

[Jyotsna Umesh]

hi,
But I don't understand why even "Exception 1 caught" line is printed becoz the string that was passed was not null, it was later on ,in the method made null, so why it goes in catch 'nullpointer exception' ?
Thanks in advance,
Jyotsna

[Jyotsna Umesh]

After giving a second thought I got it.
It is actually in first try since x is null, it is catched by null pointer exception, in second try block it prints true since the first condition is true and its is short circuit operator so it doesn't actually checks the second condition.
Now it goes third try block and in b now takes value false so the right ans. should be
Exception 1 caught
true
false
which is I think option 2.
Can anybody please justify this ans.
Jyotsna

[Vanitha Sugumaran]

Hi,
I think choice #4 is correct.
See the comments.

class Test {
static String s="Java";
boolean b; 
Test() {
super();
}
Test(String x) {
x=null; 
try {
if ( b=(s.length() == 4) && (x.length() == 4)) 
//b is assigned to true, so && operator evaluates x.length()
//catches Null pointer so skips this print statement
System.out.println(b);
}
catch(java.lang.NullPointerException e) {
//catches the expection and prints "Exception 1 caught"
System.out.println("Exception 1 caught"); 
}
try { 
if ( b=(s.length() == 4) | | (x.length() == 4)) 
/* b is true, so | | skips evaluating x.length() so no exception is thrown , prints the value of b*/
System.out.println(b);
}
catch(java.lang.NullPointerException e) {
System.out.println("Exception 2 caught"); 
}
try {
if ( b=(s.length() != 4) && (x.length() == 4)) 
/* b is assigned to false so && skips the second operand so no exception is thrown,the if condition is false so it skips the 
print statement*/
System.out.println(b);
}
catch(java.lang.NullPointerException e) {
System.out.println("Exception 3 caught"); 
}
} 
public static void main(String [] args) {
Test t = new Test(s);
}
}

hope this helps,
Vanitha.

[This message has been edited by Vanitha Sugumaran (edited June 17, 2001).]

[Jyotsna Umesh]

Thanks Vanitha, I missed the point. Its clear now.
Jyotsna

[jordan gong]

Thanks a lot!
I got it now, I made a mistake at the "if()".
jordan