Multiple choice technology programming languages

Given: 1. class Convert { 2. public static void main(String[] args) { 3. Long xL = new Long(456L); 4. long x1 = Long.valueOf("123"); 5. Long x2 = Long.valueOf("123"); 6. long x3 = xL.longValue(); 7. Long x4 = xL.longValue(); 8. Long x5 = Long.parseLong("456"); 9. long x6 = Long.parseLong("123"); 10. } 11. } Which will compile using Java 5, but will NOT compile using Java 1.4? (Choose all that apply.)

  1. Line 4

  2. Line 5

  3. Line 6

  4. Line 7

  5. Line 8

  6. Line 9
Reveal answer Fill a bubble to check yourself
A,D,E Correct answer
Explanation

Java 5 introduced autoboxing and unboxing. In Java 1.4, assigning a primitive long to a Long object (Lines 7 and 8) or assigning a Long object to a primitive long (Line 4) without explicit conversion would fail to compile. These lines compile in Java 5 due to automatic boxing and unboxing.

AI explanation

To determine which lines will compile using Java 5 but not Java 1.4, let's analyze each line of code:

Line 4: long x1 = Long.valueOf("123"); This line will compile in both Java 5 and Java 1.4. The valueOf method returns a Long object, which can be assigned to a long variable.

Line 5: Long x2 = Long.valueOf("123"); This line will compile in both Java 5 and Java 1.4. Similar to line 4, the valueOf method returns a Long object, which can be assigned to a Long variable.

Line 6: long x3 = xL.longValue(); This line will compile in both Java 5 and Java 1.4. The longValue method returns a long value, which can be assigned to a long variable.

Line 7: Long x4 = xL.longValue(); This line will NOT compile in Java 1.4 but will compile in Java 5. In Java 1.4, the longValue method returns a long value, which cannot be directly assigned to a Long variable. In Java 5, it will automatically be boxed into a Long object.

Line 8: Long x5 = Long.parseLong("456"); This line will NOT compile in Java 1.4 but will compile in Java 5. In Java 1.4, the parseLong method returns a long value, which cannot be directly assigned to a Long variable. In Java 5, it will automatically be boxed into a Long object.

Line 9: long x6 = Long.parseLong("123"); This line will compile in both Java 5 and Java 1.4. The parseLong method returns a long value, which can be assigned to a long variable.

Based on the explanations above, the lines that will compile using Java 5 but will NOT compile using Java 1.4 are:

A. Line 4 D. Line 7 E. Line 8

Therefore, the correct answer is A, D, and E.

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