我根据deitel的《 Java How to program》一书创建了一个程序。在第3章“有所作为”中，练习说：
（目标心率计算器）创建一个称为HeartRates的类。的 班级属性应包括此人的名字，姓氏和出生日期（由单独的 出生月份，日期和年份的属性）。您的班级应该有一个接收 此数据作为参数。为每个属性提供set和get方法。班上也应该 包括一种计算并返回该人的年龄（以年为单位）的方法，一种计算和 返回该人的最大心率以及一种计算并返回该人的目标的方法 心率。编写一个Java应用程序以提示输入该人的信息，实例化一个对象 类HeartRates并打印该对象的信息，包括该人的名字， 姓氏和出生日期-然后计算并打印该人的年龄（以年为单位），最大心脏 率和目标心率范围。
所以我写了这段代码：
// File: HeartRates.java
public class HeartRates {
private String firstName;
private String lastName;
private int month;
private int day;
private int year;
// constructor
public HeartRates( String fName, String lName, int aMonth,
int aDay, int aYear) {
firstName = fName;
lastName = lName;
month = aMonth;
day = aDay;
year = aYear;
}
// method to set first name
public void setFirstName( String fName ) {
firstName = fName;
}
// method to get first name
public String getFirstName() {
return firstName;
}
// method to set last name
public void setLastName( String lName ) {
lastName = lName;
}
// method to get last name
public String getLastName() {
return lastName;
}
// method to set month
public void setMonth( int aMonth ) {
month = aMonth;
}
// method to get month
public int getMonth() {
return month;
}
// method to set day
public void setDay( int aDay ) {
day = aDay;
}
// method to get day
public int getDay() {
return day;
}
// method to set year
public void setYear( int aYear ) {
year = aYear;
}
// method to get year
public int getYear() {
return year;
}
// returns person's age
public int ageInYears() {
return 2018 - getYear();
}
// returns maximum heart rate
public int maxHeartRate() {
return 220 - ageInYears();
}
// display target heart rate
public String targetHeartRate() {
// targetHeartRate = range 50% - 85% of maxheartrate
double fifty = 0.5 * maxHeartRate();
double eightyFive = 0.85 * maxHeartRate();
String target = (int)fifty + " BPM - " + (int)eightyFive + " BPM\n";
return target;
}
} // end class HeartRates
和另一个类对其进行测试：
// File: HeartRatesTest.java
// Testing heart rate class
import java.util.Scanner;
public class HeartRatesTest {
public static void main(String[] args) {
Scanner input = new Scanner( System.in );
HeartRates profile = new HeartRates();
String firstName;
String lastName;
int month;
int day;
int year;
// collecting user's information
System.out.print("Enter your first name: ");
firstName = input.nextLine();
profile.setFirstName( firstName );
System.out.print("Enter your last name: ");
lastName = input.nextLine();
profile.setLastName( lastName );
System.out.print("Enter your date of birth(month day year): ");
month = input.nextInt();
profile.setMonth( month );
day = input.nextInt();
profile.setDay( day );
year = input.nextInt();
profile.setYear( year );
// displaying user's information
System.out.printf( "\nFirst Name: %s\n", profile.getFirstName() );
System.out.printf( "Last Name: %s\n", profile.getLastName() );
System.out.printf( "Date of birth: %d\\%d\\%d\n",
profile.getMonth(), profile.getDay(), profile.getYear() );
System.out.printf( "Age: %d\n", profile.ageInYears() );
System.out.printf( "Maximum heart rate: %d BPM\n", profile.maxHeartRate() );
System.out.printf( "Target heart rate: " + profile.targetHeartRate() );
} // end method main
} // end class HeartRateTest
但我收到此错误消息：
HeartRatesTest.java:10: error: constructor HeartRates in class
HeartRates cannot be applied to given types;
HeartRates profile = new HeartRates();
^ required: String,String,int,int,int
found: no arguments reason: actual and
formal argument lists differ in length 1 error
但是我不知道为什么要我放String，String，int，int，int。 谁能帮我解决此错误？
答案 0 :(得分：0)
类public HeartRates( String fName, String lName, int aMonth, int aDay, int aYear)的构造函数HeartRates具有参数String,String,int,int,int。
所以您必须在
中提供这些值HeartRates profile = new HeartRates(); // need values as argument
类似：-
// calling constructor with arguments
HeartRates profile = new HeartRates(firstName, lastName, month, day, year);
修改后的HeartRatesTest.java
// File: HeartRatesTest.java
// Testing heart rate class
import java.util.Scanner;
public class HeartRatesTest {
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
String firstName;
String lastName;
int month;
int day;
int year;
// collecting user's information
System.out.print("Enter your first name: ");
firstName = input.nextLine(); // no need of setFirstName()
System.out.print("Enter your last name: ");
lastName = input.nextLine(); // no need of setLastName()
System.out.print("Enter your date of birth(month day year): ");
month = input.nextInt(); // no need of setMonth()
day = input.nextInt(); // no need of setDay()
year = input.nextInt(); // no need of setYear()
/* Object of HeartRates is defined after reading all values */
HeartRates profile = new HeartRates(firstName, lastName, month, day, year); // calling constructor with arguments
// displaying user's information
System.out.printf("\nFirst Name: %s\n", profile.getFirstName());
System.out.printf("Last Name: %s\n", profile.getLastName());
System.out.printf("Date of birth: %d\\%d\\%d\n", profile.getMonth(), profile.getDay(), profile.getYear());
System.out.printf("Age: %d\n", profile.ageInYears());
System.out.printf("Maximum heart rate: %d BPM\n", profile.maxHeartRate());
System.out.printf("Target heart rate: " + profile.targetHeartRate());
} // end method main
} // end class HeartRateTest
正确使用构造函数时，不需要使用那些set-functions。每次数据插入都可以由构造函数完成。
输出：-
Enter your first name: abc
Enter your last name: def
Enter your date of birth(month day year): 12 25 1998
First Name: abc
Last Name: def
Date of birth: 12\25\1998
Age: 20
Maximum heart rate: 200 BPM
Target heart rate: 100 BPM - 170 BPM