Question

在构建一个变量已经具有默认值的构造函数时，我遇到很多问题，然后调用稍后在TestGuitar类中设置的新变量。我已经成功编译了程序并打印了默认值。我没有成功保留尝试在TestGuitar类的newGuitar变量中设置的新变量。我知道所有问题都来自我的构造函数。在这种情况下，我需要一个0 arg构造函数来创建默认吉他，并需要一个新的构造函数来创建非常特定的吉他。

我为默认吉他设置了一些私有变量。如果我从不将任何内容传递给TestGuitar类中的newGuitar变量，我希望程序返回默认变量。如果我确实传递了一些东西，即guitarLength 24.75，我希望我的程序返回该值。更进一步，我希望该新变量可由getter方法调用。我相信我有75％的解决方案，但我需要专门针对构造函数问题的帮助。我只是认为我对构造函数的概念不够了解，无法同时包含0 arg和特定的构造函数。

//File name: Guitar.java
//Autor: Michael Joy
//Date: 09/16/2018
//Purpose: Building and testing guitar objects

import java.awt.Color;
import java.util.*;
import java.util.Random;

class Guitar {
    //defines the default values for our default guitar if we do not pass anything new to the object
    private int numStrings = 6;
    private double guitarLength = 28.2;
    private String guitarManufacturer = "Gibson";
    private Color guitarColor = Color.RED;
    private static int i = 1;
    private static Random rand = new Random();

    //declaring the constructor
    public Guitar (){
        //all my problems coming from here
        this.numStrings = numStrings;
        this.guitarLength = guitarLength;
        this.guitarManufacturer = guitarManufacturer;
        this.guitarColor = guitarColor;
    }

    public Guitar (int strings, double length, String manufacturer, Color color){
        //more problems here
         strings = this.numStrings;
         length = this.guitarLength;
         manufacturer = this.guitarManufacturer;
         color = this.guitarColor;
         System.out.printf("toString: %s \n ", this);
    }

    public int getNumStrings() {
      return numStrings;
    }

    public double getGuitarLength() {
      return guitarLength;
    }

    public String getGuitarManufacturer() {
      return guitarManufacturer;
    }

    public Color getGuitarColor(){
      return this.guitarColor;
    }

    public static void playGuitar(){
        String[] musicNotes = {"A", "B", "C", "D", "E", "F", "G"};
        String[] musicDuration = {"(0.25)","(0.5)","(1)", "(2)","(4)"};
         System.out.print("playGuitar: ");
         for (i = 1; i < 17; i++){
            int index1 = rand.nextInt(musicNotes.length);
            int index2 =  rand.nextInt(musicDuration.length);
            System.out.print(musicNotes[index1]);
            System.out.print(musicDuration[index2] + ",");
            }
         }

    public String toString(){
        return String.format("%d, %f, %s, %s", numStrings, guitarLength, guitarManufacturer, guitarColor);
    }
}

class TestGuitar extends Guitar{
        public static void main (String args[] ){
          Guitar newGuitar = new Guitar(6, 24.75, "Les Paul", Color.white);
          playGuitar();
  }
}

Answer 1

class Guitar {
private static int i = 1;
private static Random rand = new Random();
private int numStrings;
private double guitarLength ;
private String guitarManufacturer;
private Color guitarColor;

//declaring the constructor
public Guitar (){
    //all my problems coming from here
    numStrings = 6;
    guitarLength = 28.2;
    guitarManufacturer = "Gibson";
    guitarColor = Color.RED;
}

public Guitar (int strings, double length, String manufacturer, Color color){
    this.numStrings = Strings;
    this.guitarLength = length;
    this.guitarManufacturer = manufacturer;
    this.guitarColor = color;
     System.out.printf("toString: %s \n ", this);
}
public int getNumStrings() {
  return numStrings;
}

public double getGuitarLength() {
  return guitarLength;
}

public String getGuitarManufacturer() {
  return guitarManufacturer;
}

public Color getGuitarColor(){
  return this.guitarColor;
}

public static void playGuitar(){
    String[] musicNotes = {"A", "B", "C", "D", "E", "F", "G"};
    String[] musicDuration = {"(0.25)","(0.5)","(1)", "(2)","(4)"};
     System.out.print("playGuitar: ");
     for (i = 1; i < 17; i++){
        int index1 = rand.nextInt(musicNotes.length);
        int index2 =  rand.nextInt(musicDuration.length);
        System.out.print(musicNotes[index1]);
        System.out.print(musicDuration[index2] + ",");
        }
     }

public String toString(){
    return String.format("%d, %f, %s, %s", numStrings, guitarLength, guitarManufacturer, guitarColor);
}
}

您还可以使用1个构造器：

public Guitar (int strings=6, double length=28.2, String manufacturer="Gibson", Color color=Color.RED){
        this.numStrings = Strings;
        this.guitarLength = length;
        this.guitarManufacturer = manufacturer;
        this.guitarColor = color;
         System.out.printf("toString: %s \n ", this);
    }

Answer 2

您的默认初始值属于no-args构造函数。然后，您需要更正在第二个构造函数中分配值的顺序。喜欢，

private int numStrings;
private double guitarLength;
private String guitarManufacturer;
private Color guitarColor;
private static int i = 1;
private static Random rand = new Random();

// declaring the constructor
public Guitar() {
    this.numStrings = 6;
    this.guitarLength = 28.2;
    this.guitarManufacturer = "Gibson";
    this.guitarColor = Color.RED;
}

public Guitar(int strings, double length, String manufacturer, Color color) {
    this.numStrings = strings;
    this.guitarLength = length;
    this.guitarManufacturer = manufacturer;
    this.guitarColor = color;
    System.out.printf("toString: %s \n ", this);
}

请注意，第一个构造函数可以重写为使用其他构造函数。喜欢，

// declaring the constructor
public Guitar() {
    this(6, 28.2, "Gibson", Color.RED);
}

Java：0个arg构造函数和构造函数的问题

2 个答案: