是
#include <algorithm>
#include <iomanip>
#include <iostream>
#include <stdexcept>
#include <string>
#include <vector>
using std::cin;
using std::cout;
using std::domain_error;
using std::endl;
using std::istream;
using std::ostream;
using std::setprecision;
using std::sort;
using std::streamsize;
using std::string;
using std::vector;
// compute the median of a `vector<double>'
// note that calling this function copies the entire argument `vector'
double median(vector<double> vec)
{
#ifdef _MSC_VER
typedef std::vector<double>::size_type vec_sz;
#else
typedef vector<double>::size_type vec_sz;
#endif
vec_sz size = vec.size();
if (size == 0)
throw domain_error("median of an empty vector");
sort(vec.begin(), vec.end());
vec_sz mid = size/2;
return size % 2 == 0 ? (vec[mid] + vec[mid-1]) / 2 : vec[mid];
}
// compute a student's overall grade from midterm and final exam grades and homework grade
double grade(double midterm, double final, double homework)
{
return 0.2 * midterm + 0.4 * final + 0.4 * homework;
}
// compute a student's overall grade from midterm and final exam grades
// and vector of homework grades.
// this function does not copy its argument, because `median' does so for us.
double grade(double midterm, double final, const vector<double>& hw)
{
if (hw.size() == 0)
throw domain_error("student has done no homework");
return grade(midterm, final, median(hw));
}
// read homework grades from an input stream into a `vector<double>'
istream& read_hw(istream& in, vector<double>& hw)
{
if (in) {
// get rid of previous contents
hw.clear();
// read homework grades
double x;
while (in >> x)
hw.push_back(x);
// clear the stream so that input will work for the next student
in.clear();
}
return in;
}
int main()
{
// ask for and read the student's name
cout << "Please enter your first name: ";
string name;
cin >> name;
cout << "Hello, " << name << "!" << endl;
// ask for and read the midterm and final grades
cout << "Please enter your midterm and final exam grades: ";
double midterm, final;
cin >> midterm >> final;
// ask for the homework grades
cout << "Enter all your homework grades, "
"followed by end-of-file: ";
vector<double> homework;
// read the homework grades
read_hw(cin, homework);
// compute and generate the final grade, if possible
try {
double final_grade = grade(midterm, final, homework);
streamsize prec = cout.precision();
cout << "Your final grade is " << setprecision(3)
<< final_grade << setprecision(prec) << endl;
} catch (domain_error) {
cout << endl << "You must enter your grades. "
"Please try again." << endl;
return 1;
}
return 0;
}
正确?我想知道他们是否会引用同一个对象。此代码无法编译。但可能有几种情况需要澄清。
我怀疑这会扩展到
test::testMethod == test::testMethod
以下是否属实。
Runnable r = () -> test.testMethod()
Runnable r1 = () -> test.testMethod()
答案 0 :(得分:1)
让我们看看下面的例子:
Predicate<String> predicate = String::isEmpty;
Function<String,Boolean> function = String::isEmpty;
System.out.println(predicate.equals(function)); // false
lambda不包含任何有关它类型的信息。该信息是从上下文中推断出来的。正如我们在上面所看到的,相同的lamba String::inEmpty
可以表示不同的功能接口。
答案 1 :(得分:1)
即使您的代码可以编译并且test::testMethod
声明为Runnable
,答案test::testMethod == test::testMethod
总是返回false,因为您要比较两个diff类实例。对于每个lambda表达式,编译器将为它创建一个synthentic
匿名内部类。例如:
//a synthentic anonymous lambda class A implemented Runnable
Runnable r = () -> test.testMethod();
//a synthentic anonymous lambda class B implemented Runnable
Runnable r1 = () -> test.testMethod();
r.getClass().equals(r1.getClass());// always return false