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Two questions from javacamp

 
Greenhorn
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Question 1. Given:

1. class Test {
2. public static void main(String[] args) {
3. int len = 0, oldlen = 0;
4. Object[] a = new Object[0];
5. try {
6. for (; ; ) {
7. ++len;
8. Object[] temp = new Object[oldlen = len];
9. temp[0] = a;
10. a = temp;
11. }
12. } catch (Error e) {
13. System.out.println(e + ", " + (oldlen==len));
14. }
15. }
16. }

What will happen when you attempt to compile and run the code?

A. It prints: java.lang.OutOfMemoryError, true.
B. It prints: java.lang.OutOfMemoryError, false.
C. It will not compile because of code at line 8.
D. It will not compile because of code at line 10.
E. It will not compile because of code at line 12.

I compiled the class and the answer is A. Can someone explain why the output is OutOfMemoryError and true?

Question 2. What is the output of the following code when compiled and run?

1. public class Test {
2. public static void main(String[] args) {
3. boolean b = false;
4. String s = (b=!b)?(b=!b)?"Hello":"hello" : ( b=!b)?"world":"World";
5. System.out.println(s);
6. }
7. }

A. Prints: Hello
B. Prints: hello
C. Prints: Helloworld
D. Prints: helloWorld
E. Compilation error.

Again, I compiled the class and the answer is B. Can someone explain why the output is hello?
[ August 28, 2007: Message edited by: Tobie Henderson ]
 
Tobie Henderson
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Alright. I think I know why the first question gives OutOfMemoryError. Because the for loop is an infinite loop, it will create infinite number of Object arrays, until it runs out of memory and throws an error with oldlen = len.
 
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1. public class Test {
2. public static void main(String[] args) {
3. boolean b = false;
4. String s = (b=!b)?(b=!b)?"Hello":"hello" : ( b=!b)?"world":"World";
5. System.out.println(s);
6. }
7. }

For ternary operator it evaluates from right to left.
 
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The second one appears to be setting the value b to the opposite value. For example (b=!b) is saying set false = !false. So it is true. Then the program does it again so it sets true = !true so it is false which would make it arrive at "hello". Hope this makes sense.
 
Tobie Henderson
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Originally posted by raghu nagabandi:

For ternary operator it evaluates from right to left.



Can you please elaborate? Which b=!b is evaluated first, the leftmost, the one in the middle, or the rightmost? And after evaluating a b=!b condition, which String does it go to, "hello", "Hello", "world", or "World"?
 
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