[Java] OCP題庫 －Array陣列

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題目－＞答案－＞個人解題方式－＞重點整理

【題目】

1.

Which two array initialization statements are valid?

A.int array[3] = new int[] {1, 2, 3};

B.int array[] = new int[] {1,2,3};

C.int array[] = new int[3];

array = {1, 2, 3};

D.int array[] = new int[3] {1, 2, 3};

E.int array[] = new int[3];

array[0] = 1;

array[1] = 2;

array[2] = 3;

2.

Given the code fragment:

String shirts[][] = new String[2][2];

shirts[0][0] = “red”;

shirts[0][1] = “blue”;

shirts[1][0] = “small”;

shirts[1][1] = “medium”;

Which code fragment prints red:blue:small:medium:?

A)

for (String[] c : shirts) {

for (String s : c) {

System.out.print(s + “:”);

}

}

B)

for (int index = 1; index < 2; index++) {

for (int idx = 1; idx < 2; idx++) {

System.out.print(shirts[index][idx] + “:”);

}

}

C)

for (int index = 0; index < 2; ++index) {

for (int idx = 0; idx < index; ++idx) {

System.out.print(shirts[index][idx] + “:”);

}

}

D)

for (int index = 0; index <= 2;) {

for (int idx = 0; idx <= 2;) {

System.out.print(shirts[index][idx] + “:”);

}

index++;

}

3.

Given:
public class Test {
public static void main(String[] args) {
String[][] chs = new String[5][2];
chs[0] = new String[2];
chs[1] = new String[5];
int i = 97;
for (int a = 0; a < chs.length; a++) {
for (int b = 0; b < chs.length; b++) {
chs[a][b] = "" + i;
i++;
}
}
for (String[] ca : chs) {
for (String c : ca) {
System.out.print(c + " ");
}
System.out.println();
}
}
}
What is the result?
A. NullPointerException is thrown at runtime.//呼叫的變數沒有值
B.
97 98
99 100 null null null
C.
97 98
99 100 101 102 103
D.
Compilation fails.
E.
An ArrayIndexOutOfBoundsException is thrown at runtime.

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【答案】

1.B.E

2.A

3.E

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【個人解題方式】

主要講解第三題

3.因為空間不夠

chs[0] = new String[2];//chs項下只有2個，chs[0][0]、chs[0][1]
chs[1] = new String[5];
for (int a = 0; a < chs.length; a++) {
for (int b = 0; b < chs.length; b++) {
chs[a][b] = "" + i;
i++;
}
}

所以在這段程式碼的時候，會在

chs[0][0]、chs[0][1]、chs[0][2]……chs[0][4]放值進去

可是跑到chs[0][2]的時候，因為沒有宣告這個陣列，所以會跑出沒有陣列空間的Exception。

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