Java-基础题目集-Chapter 2，3 Elementary Programming， Selections

一.单选

1.Math.pow(2, 3) returns _____（D）_____.

A.9

B.8

C.9.0

D.8.0

2.Are the following four statements equivalent?（A）

  number += 1;
  number = number + 1;
  number++;
  ++number;

A.Yes

B.No

3.Analyze the following code fragments that assign a boolean value to the variable even.（E）

Code 1:

if (number % 2 == 0)
  even = true;
else
  even = false;

Code 2:

even = (number % 2 == 0) ? true: false;

Code 3:

even = number % 2 == 0;

A.Code 2 has a compile error, because you cannot have true and false literals in the conditional expression.

B.Code 3 has a compile error, because you attempt to assign number to even.

C.All three are correct, but Code 1 is preferred.

D.All three are correct, but Code 2 is preferred.

E.All three are correct, but Code 3 is preferred.

4.What is 1 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1 == 0.5?（C）

A.true

B.false

C.There is no guarantee that 1 - 0.1 - 0.1 - 0.1 - 0.1 - 0.1 == 0.5 is true.

解析：由于表达式涉及浮点数，并且浮点数是近似的，浮点数不能直接使用==进行比较

5.Suppose x=10 and y=10. What is x after evaluating the expression (y > 10) && (x-- > 10)?（B）

A.9

B.10

C.11

6.Suppose x=10 and y=10. What is x after evaluating the expression (y > 10) && (x++ > 10).（B）

A.9

B.10

C.11

解析：&&是短路操作符，

为什么被称为短路运算符？

这是因为一旦可以确定结果，解析就会停止。解析的顺序是从左至右，所以后边运算不执行，因此被形象的称作短路。

二.多选

1.Which of the following assignment statements is incorrect?（CD）

A.i = j = k = 1;

B.i = 1; j = 1; k = 1;

C.i = 1 = j = 1 = k = 1;

D.i == j == k == 1;

2.Which of the following are so called short-circuit operators?（AC）

A.&&

B.&

C.||

D.|

解析：以下是所谓的短路操作符：&& ，||

3.What is the possible output from System.out.println((Math.random() * 4))?（ABCD）

A.0

B.1

C.2

D.3

E.4

解析：Math.random() 函数返回一个浮点数，伪随机数在范围从0 到小于1，也就是说，从 0（包括 0）往上，但是不包括 1（排除 1），然后您可以缩放到所需的范围。实现将初始种子选择到随机数生成算法;它不能被用户选择或重置。