Question

import java.util.*;


// This program will estimate the cost to paint a room in your house

public class PaintJobEstimator {

    // square feet per one gallon of paint.
    public static final double AREA_PER_GALLON = 112.0; 

    // hours of labor needed to paint AREA_PER_GALLON square feet.
    public static final double HOURS_PER_UNIT_AREA = 8.0;

    // charge to customer for one hour of labor.
    public static final double LABOR_COST_PER_HOUR = 35.0;

    // main declares a Scanner that is passed to
    // the input methods. main also controls the
    // order of calculations.
    public static void main( String[] args ) {
        Scanner keyboard = new Scanner( System.in );

        // How many square feet do we need to paint?
        double sqft = getInput( keyboard, 
                       "Enter the number of square feet: " );

        // How much does a gallon of paint cost?
        double gallonCost = getInput( keyboard, 
                       "Enter the price of a gallon of paint: " );        
        ////////////////////////////////////////
        // Calculate the cost of this paint job.
        ////////////////////////////////////////

        // First, how many gallons of paint do we need?
        int numGallons = calculateGallons( sqft );

        // How long will the job take?
        double hoursLabor = calculateHours( sqft );

        // How much will the paint cost?
        double paintCost = calculatePaintCost( numGallons, gallonCost );

        // How much will the labor cost?
        double laborCost = calculateLaborCost( hoursLabor );

        // What's the total bill?
        double totalCost = calculateTotalCost( paintCost, laborCost );

        // Print the results.
        generateReport( sqft, gallonCost, numGallons, hoursLabor, 
                        paintCost, laborCost, totalCost);

    }

    public static double getInput( Scanner input, String prompt ) {
        System.out.print( prompt );
        while ( !input.hasNextDouble() ) {
            input.nextLine(); // get rid of bad input.
            System.out.print( prompt );
        }
        double inValue = input.nextDouble();
        input.nextLine(); // clear the input line.
        return inValue;
    }


    // Your methods go here:

    // calculateGallons
    public static int calculateGallons( double sqft ) {
        // TO DO return correct value
        return (int)Math.ceil(sqft / AREA_PER_GALLON);
    } 

    // calculateHours
    public static double calculateHours( double sqft ) {
        // TO DO return correct value
        return sqft / 14;
    }

    // TO DO: calculatePaintCost
    public static double calculatePaintCost (int numGallons, double gallonCost){
        return numGallons * gallonCost;
    }

    // TO DO: calculateLaborCost (Hours * Labor/hr)
    public static double calculateLaborCost( double hoursLabor ){
        return hoursLabor * LABOR_COST_PER_HOUR;
    }    
    // TO DO: calculateTotalCost
    public static double calculateTotalCost( double paintCost, double laborCost ){
        return paintCost + laborCost;
    }

    // To Do: generateReport
    public static double generateReport(double sqft,  double gallonCost, int numGallons, double hoursLabor, double paintCost, double laborCost, double totalCost) {
        return  System.out.print("To paint" + sqft + "square feet, with"); 
                System.out.print("paint that costs" + gallonCost + "per gallon,"); 
                System.out.print("you will need" + numGallons + "gallons of paint"); 
                System.out.print("and" + hoursLabor + "hours of labor."); 
                System.out.print("The cost of the paint is: " + paintCost ); 
                System.out.print("The cost of the labor is: "+ laborCost); 
                System.out.print("The total cost of the job is: " + totalCost); 
        System.out.println();
    }




}

我使用generateReport方法，我不知道如何正确返回它。我一直收到错误

PaintJobEstimator.java:99: error: incompatible types: void cannot be              converted to double      
    return  System.out.print("To paint" + sqft + "square feet, with"); 
                            ^

我在做错了什么。或者我完全忽略了这一点。我是新手，真的需要帮助，我不想得到答案但是如果有人可以指出我的方向很好

Answer 1

System.out.print()不返回任何值;它的返回类型为void。

为了在没有任何错误的情况下重写它，请将其更改为：

public static void generateReport(double sqft,  double gallonCost, int numGallons, double hoursLabor, double paintCost, double laborCost, double totalCost) {
            System.out.print("To paint" + sqft + "square feet, with"); 
            System.out.print("paint that costs" + gallonCost + "per gallon,"); 
            System.out.print("you will need" + numGallons + "gallons of paint"); 
            System.out.print("and" + hoursLabor + "hours of labor."); 
            System.out.print("The cost of the paint is: " + paintCost ); 
            System.out.print("The cost of the labor is: "+ laborCost); 
            System.out.print("The total cost of the job is: " + totalCost); 
            System.out.println();

Answer 2

System.out.print(...)打印给定对象输出。 return用于将值传递给函数的调用者，在本例中为main方法。由于您的generateReport方法属于double类型，因此您必须返回一些double值。如果您不想返回任何内容，那么您的方法应为void。

例如，

System.out.print(...)是一个void函数。

错误：不兼容的类型：void无法转换为double

2 个答案: