Java中的setter和getter的意义是什么?
请原谅它的长度,但是这里有两个程序,两者完全相同,但是一个有一个没有setter,getter和构造函数的程序。
我之前已经学过一个基本的C ++类,并且不记得其中的任何一个,而现在我还没有看到它们的意义,如果有人可以用拉面的术语来解释它们的话,我将不胜感激。目前,它们似乎不过是浪费空间,以使我的代码看起来更长,但是老师说它们很重要(到目前为止,就是这样)。
提前致谢!现在是代码:Mileage.java:
package gasMileage;import java.util.Scanner; //program uses class Scanner
public class Mileage
{
public int restart;
public double miles, gallons, totalMiles, totalGallons, milesPerGallon;
public Mileage(int newRestart, double newMiles, double newGallons,
double newTotalMiles, double newTotalGallons, double newMilesPerGallon)
{
setRestart(newRestart);
setMiles(newMiles);
setGallons(newGallons);
setTotalMiles(newTotalMiles);
setTotalGallons(newTotalGallons);
setMilesPerGallon(newMilesPerGallon);
}
public void setRestart(int newRestart)
{
restart = newRestart;
}
public int getRestart()
{
return restart;
}
public void setMiles(double newMiles)
{
miles = newMiles;
}
public double getMiles()
{
return miles;
}
public void setGallons(double newGallons)
{
gallons = newGallons;
}
public double getGallons()
{
return gallons;
}
public void setTotalMiles(double newTotalMiles)
{
totalMiles = newTotalMiles;
}
public double getTotalMiles()
{
return totalMiles;
}
public void setTotalGallons(double newTotalGallons)
{
totalGallons = newTotalGallons;
}
public double getTotalGallons()
{
return totalGallons;
}
public void setMilesPerGallon(double newMilesPerGallon)
{
milesPerGallon = newMilesPerGallon;
}
public double getMilesPerGallon()
{
return milesPerGallon;
}
public void calculateMileage()
{
Scanner input = new Scanner(System.in);
while(restart == 1)
{
System.out.print("Please input number of miles you drove: ");
miles = input.nextDouble();
totalMiles = totalMiles + miles;
System.out.print("Please input number of gallons you used: ");
gallons = input.nextDouble();
totalGallons = totalGallons + gallons;
milesPerGallon = miles / gallons;
System.out.printf("Your mileage is %.2f MPG.\n", milesPerGallon);
System.out.print("Would you like to try again? 1 for yes, 2 for no: ");
restart = input.nextInt();
}
milesPerGallon = totalMiles / totalGallons;
System.out.printf("Your total mileage for these trips is: %.2f.\nYour total gas consumed on these trips was: %.2f.\n", totalMiles, totalGallons);
System.out.printf("Your total mileage for these trips is: %.2f MPG", milesPerGallon);
}
}
Mileagetest.java:
package gasMileage;public class Mileagetest
{
public static void main(String[] args)
{
Mileage myMileage = new Mileage(1,0,0,0,0,0);
myMileage.calculateMileage();
}
}
现在,对于那些没有二传手的人:
Testmileage.java:package gasMileage;
import java.util.Scanner;
public class Testmileage
{
int restart = 1;
double miles = 0, milesTotal = 0, gas = 0, gasTotal = 0, mpg = 0;
Scanner input = new Scanner(System.in);
public void testCalculate()
{
while(restart == 1)
{
System.out.print("Please input miles: ");
miles = input.nextDouble();
milesTotal = milesTotal + miles;
System.out.print("Please input gas: ");
gas = input.nextDouble();
gasTotal = gasTotal + gas;
mpg = miles/gas;
System.out.printf("MPG: %.2f", mpg);
System.out.print("\nContinue? 1 = yes, 2 = no: ");
restart = input.nextInt();
}
mpg = milesTotal / gasTotal;
System.out.printf("Total Miles: %.2f\nTotal Gallons: %.2f\nTotal MPG: %.2f\n", milesTotal, gasTotal, mpg);
}
}
Testmileagetest.java:
package gasMileage;
public class Testmileagetest
{
/**
* @param args
*/
public static void main(String[] args)
{
Testmileage test = new Testmileage();
test.testCalculate();
}
}
再次感谢!
回答:
无论哪种语言,getter和setter的目的都是隐藏基础变量。这样,您可以在尝试设置值时添加验证逻辑-例如,如果您有一个出生日期字段,则可能只希望将该字段设置为过去的某个时间。如果该字段是公共可访问和可修改的,则不能强制执行此操作-您需要使用getter和setter。
即使您不需要任何验证,将来也可能需要它。现在,编写getter和setter意味着接口保持一致,因此更改现有代码不会中断。
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