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| No. | Answer | Remark | |
|---|---|---|---|
| 1 | a | Prints: 3,4,8 | An array variable a1 is declared, and the declaration contains the initializer {{1,2,3},{4,5,6},{7,8,9,10}}. The initializer creates an array containing three components, and each is a reference to a subarray of type int[]. Each subarray contains components of type int, so the elements of the array referenced by a1 are of type int. The array access expression, a1[0][2] = a1[1st subarray][third component] = 3. |
| 2 | e | Prints: 2,5,9 | The declarations of the array variables, a1, a2 and a3, are different in terms of the position of the square brackets, but each is of type int[][]. The array access expression, a1[0][1] = a[1st subarray][2nd component] = 2. Each of the three array variable declarations has an array initializer. The same initializer, {{1,2},{3,4,5},{6,7,8,9}}, is used in each of the three cases. The initializer specifies three components of type int[], so each component is a reference to an array object containing components of type int. The size of each of the subarrays is different: The size of the first is 2, the second is 3, and the third is 4. |
| 3 | f | Compile-time error | The array initializer, {{1;2};{3;4;5};{6;7;8;9}} generates a compile-time error, because the commas have been replaced by semicolons. The array initializer should have been specified as follows: {{1,2},{3,4,5},{6,7,8,9}}. |
| 4 | f | Compile-time error | The array initializer, ((1,2),(3,4,5),(6,7,8,9)), generates a compile-time error, because the curly braces have been replaced by parentheses. The array initializer should have been specified as follows: {{1,2},{3,4,5},{6,7,8,9}}. |
| 5 | f | Compile-time error | The array initializer, [[1,2],[3,4,5],[6,7,8,9]], generates a compile-time error, because the curly braces have been replaced by square brackets. The array initializer should have been specified as follows: {{1,2},{3,4,5},{6,7,8,9}}. |
| 6 | e | Prints: 2,5,9 | The line marked 1 declares three array variables, a2, a3 and a4, and each references an array with components of type int. The line marked 2 declares an array variable, a1, where each component is initialized with a reference to one of the previously created arrays. The array access expression, a1[0][1], is evaluated as follows: a1[0][1] = a1[first subarray][second component] = 2. |
| 7 | a | 1 | A compile-time error occurs at the line marked 1, because the array variable declaration can not be used to specify the number of components contained in the array. Instead, the dimension expression should be contained in an array creation expression such as the following, new int[3]. |
| 8 | b | 2 | An array variable is declared by placing brackets after the identifier or after the type name. A compile-time error occurs at the line marked 2, because the brackets appearing before the identifier for array variable a4 are not associated with the type or the identifier. |
| 9 | e | Prints: 2,3,5 | Each of the three array variable declarations, a1, a2 and a3, is different in terms of the position of the square brackets, but each declares a variable of type int[][]. Each of the three declarations contains an array initializer. In each case, the initializer could be simplified as follows: {{1,2},{3,4,5}}. The initializer creates an array containing two components, and each is a reference to an array containing components of type int. The size of each of the subarrays is different: The size of the first is 2 and the second is 3. The array access expression, a1[0][1] = a[1st subarray][2nd component] = 2. |
| 10 | c | Prints: 4 | The array initializer, {{1,2},{3,4,5},{6,7,8,9},{}}, creates an array containing four components, and each is a reference to a subarray of type int[]. The size of the array referenced by variable a1, is 4, because a1 contains four components. The size of the first subarray is 2, the second is 3, the third is 4 and the fourth is zero. |
| 11 | a | Prints: 2,3,4,0, | The array initializer, {{1,2},{3,4,5},{6,7,8,9},{}}, creates an array containing four components, and each is a reference to an array of type int[]. The size of the first subarray is 2, the second is 3, the third is 4, and the fourth is zero. While the components of the array referenced by a1 are of type int[], the elements of the array referenced by a1 are of type int. |
| 12 | b | Prints: 147258369 | The array variable a1 is declared with the initializer, {{1,2,3},{4,5,6},{7,8,9}}. The array access expression, a1[0][1] = a1[first subarray][second element] = 2. If the argument of the print statement had been a1[i][j] then the output would have been 123456789. The tricky feature of this question is the reversal of i and j to produce the deceptive array access expression, a1[j][i]. The output is 147258369. |
| 13 | b | Prints: A11 | The declaration A11[] a1 = new A11[1] declares a variable a1 that references an array that contains one component of type A11. The declaration A11[][] a2 = new A11[2][] declares a variable a2 that references an array that contains two components of type A11[]. In other words, the array referenced by a2 contains two reference variables, and each is able to reference a subarray. The initial value of the subarray references is null. The size of the subarrays has not been specified. The declaration A11[][][] a3 = new A11[3][][] declares a variable a3 that references an array that contains three components of type A11[][]. In other words, the array referenced by a3 contains three reference variables, and each is able to reference a subarray. The initial value of each subarray reference is null. The dimensions of the subarrays have not been specified. At line 5, a reference to the array referenced by a1 is assigned to each of the two components of the array referenced by a2, a2[0] = a2[1] = a1. At line 6, a reference to the array referenced by a2 is assigned to each of the three components of the array referenced by a3, a3[0] = a3[1] = a3[2] = a2. In other words, after line 6, each component of the array referenced by a3 is a reference to the array referenced by a2, and each element of the array referenced by a2 is a reference to the array referenced by a1, and the array referenced by a1 contains a reference to an instance of class A11. Every element of the multi-dimensional array referenced by a3 contains a reference to a single instance of class A11. The print method invokes the toString method on the instance, and produces the output, A11. |
| 14 | a k | Prints: null Run-time error | The declaration A13[] a1 = new A13[1] declares a variable a1 that references an array that contains one component of type A13. The declaration A13[][] a2 = new A13[2][1] declares a variable a2 that references an array that contains two components of type A13[]. In other words, the array referenced by a2 contains two references to two subarrays of type A13[]. The size of each subarray is 1. The declaration A13[][][] a3 = new A13[3][3][3] declares a variable a3 that references an array that contains three components of type A13[][]. In other words, the array referenced by a3 contains three references to three subarrays of type A13[][]. The dimensions of the subarrays are 3 X 3. The dimensions of the array referenced by a3 are 3 X 3 X 3. The number of elements in the array referenced by a3 is 3 * 3 * 3 = 27 elements. Each of the three subarrays contains three components, where each is a reference to a subarray of type A13[]. Each of the 27 elements of the array referenced by a3 is a reference of type A13 that has been initialized to the default value of null. At line 7, a reference to the array referenced by a2 is assigned to each of the three components of the array referenced by a3, a3[0] = a3[1] = a3[2] = a2. Since the array referenced by a2 has dimensions 2 X 1, the array referenced by a3 now has dimensions 3 X 2 X 1. The number of elements is 6. An attempt to access any element beyond those 6 results in an exception at run-time. |