如何從一個類訪問ArrayList的特定部分到另一個類

Question

package HW1; 

import java.util.ArrayList; 

public class Arrays { 
public ArrayList Case() { 
    ArrayList <Case> cases = new ArrayList<Case>(); 
    Case c1 = new Case("Antec Twelve Hundred V3", 20.20, 8.39, 22.87, "ATX Full   Tower", 154.99); 
    Case c3 = new Case("BitPhenix Phenom M Arctic", 9.80, 12.95, 14.69, "MicroATX Mini Tower", 89.99); 
    Case c2 = new Case("Corsair 250D", 13.8, 10.9, 11.4, "MiniITX Tower", 99.9); 


    cases.add(c1); 
    cases.add(c2); 
    cases.add(c3); 

    for (int i = 0; i < cases.size(); i++) { 
     System.out.println("Name: " + cases.get(i).getName() + "\n" + "Dimensions: " + cases.get(i).getLength() + "' x " + cases.get(i).getWidth() + "' x " + cases.get(i).getHeight() + "' " + "Type: " +cases.get(i).getType() + "\n" + "Price: $" + cases.get(i).getPrice()+ "\n"); 
    } 
    return cases; 
} 

public ArrayList Monitor() { 
    ArrayList <Monitor> monitor = new ArrayList<Monitor>(); 
    Monitor m1 = new Monitor("Asus PB278Q", 27, 549.99); 
    Monitor m2 = new Monitor("Dell U2412M", 24, 263.99); 
    Monitor m3 = new Monitor("Samsung S22300H", 21.5, 139.99); 

    monitor.add(m1); 
    monitor.add(m2); 
    monitor.add(m3); 

    for (int i = 0; i < monitor.size(); i++) { 
     System.out.println("Name: " + monitor.get(i).getName() + "\n" + "Size: " + monitor.get(i).getSize() + "' " + "\n" + "Price: $" + monitor.get(i).getPrice() + "\n"); 
    } 

    return monitor; 
} 

public ArrayList CPU() { 
    ArrayList <CPU> cpu = new ArrayList<CPU>(); 
    CPU cpu1 = new CPU("AMDFX-8350", 4.0, 188.99); 
    CPU cpu2 = new CPU("Intel Core i5-3570K", 3.4, 179.99); 
    CPU cpu3 = new CPU("Intel Core i7-3770K", 3.5, 249.99); 

    cpu.add(cpu1); 
    cpu.add(cpu2); 
    cpu.add(cpu3); 

    for (int i = 0; i < cpu.size(); i++) { 
     System.out.println("Name: " + cpu.get(i).getName() + "\n" + "Speed: " + cpu.get(i).getSpeed() + "GHz " + "\n" + "Price: $" + cpu.get(i).getPrice() + "\n"); 
    } 
    return cpu; 
} 

public ArrayList VideoCard() { 
    ArrayList <VideoCard> videoCard = new ArrayList<VideoCard>(); 
    VideoCard vd1 = new VideoCard("Nvidia GeForce GTX 770", 2, 346.99); 
    VideoCard vd2 = new VideoCard("Nvidia GeForce GTX 670", 2, 333.99); 
    VideoCard vd3 = new VideoCard("AMD Radeon HD 7950", 3, 399.99); 

    videoCard.add(vd1); 
    videoCard.add(vd2); 
    videoCard.add(vd3); 

    for (int i = 0; i < videoCard.size(); i++) { 
     System.out.println("Name: " + videoCard.get(i).getName() + "\n" + "Memory Size: " + videoCard.get(i).getMemorySize() + "GB " + "\n" + "Price: $" + videoCard.get(i).getPrice() + "\n"); 
    } 
    return videoCard; 
} 

public ArrayList HardDrive() { 
    ArrayList <HardDrive> hardDrive = new ArrayList<HardDrive>(); 
    HardDrive hd1 = new HardDrive("Samsung MZ-7PD256BW", 256, 199.99); 
    HardDrive hd2 = new HardDrive("Corsair CSSD-F240GBGT-BK", 240, 206.99); 
    HardDrive hd3 = new HardDrive("Crucial CT128M4SSD1", 128, 199.95); 

    hardDrive.add(hd1); 
    hardDrive.add(hd2); 
    hardDrive.add(hd3); 

    for (int i = 0; i < hardDrive.size(); i++) { 
     System.out.println("Name: " + hardDrive.get(i).getName() + "\n" + "Memory Size: " + hardDrive.get(i).getSize() + "GB " + "\n" + "Price: $" + hardDrive.get(i).getPrice()+ "\n"); 
    } 
    return hardDrive; 
} 

public ArrayList Memory() { 
    ArrayList <Memory> memory = new ArrayList<Memory>(); 
    Memory me1 = new Memory("Corsair Vengeance", 8, 69.99); 
    Memory me2 = new Memory("G.Skill Ares Series", 16, 149.99); 
    Memory me3 = new Memory("Kingston Black Series", 8, 79.99); 

    memory.add(me1); 
    memory.add(me2); 
    memory.add(me3); 

    for (int i = 0; i < memory.size(); i++) { 
     System.out.println("Name: " + memory.get(i).getName() + "\n" + "Memory Size: " + memory.get(i).getSize() + "GB " + "\n" + "Price: $" + memory.get(i).getPrice()+"\n"); 
    } 
    return memory; 
} 

} 

比方說，我想訪問c3的價格。在同樣的方法，我可以打印它，但我想訪問另一個類的主要方法c3的價格。這是代碼。假設從菜單中，用戶輸入1並決定購買第一個選項。我得到它來打印選項，但我不知道如何訪問它的價格。

package HW1; 
import java.util.*; 
public class Main { 
public static void printMenu() 
{ 
    System.out.println("Menu"); 
    System.out.println("1: Choose a Case"); 
    System.out.println("2: Choose a Monitor"); 
    System.out.println("3: Choose a CPU"); 
    System.out.println("4: Choose a Video Card"); 
    System.out.println("5: Choose a Hard Drive"); 
    System.out.println("6: Choose a Memory"); 
    System.out.println("7: Delete Current Computer"); 
    System.out.println("8: Display Receipt"); 
    System.out.println("9: Quit program"); 
} 



public static void main(String[] args) { 
    printMenu(); 
    System.out.println("please select and option"); 
    Arrays arrays = new Arrays(); 


     Scanner in = new Scanner(System.in); 
     int choice = in.nextInt(); 
     if (choice == 1) { 
      ArrayList cases = arrays.Case(); 
      System.out.println(cases); 
      System.out.println("please select a case"); 
      if (choice == 1) { 
       System.out.println(c1.getPrice()); 
      } 
     } 


} 
} 

Answer 1

好了，你可以從array的類的Cases ...

ArrayList cases = arrays.Case(); 

接下來，你需要找出這種情況下，用戶感興趣...

int choice = -1; 
do { 

    System.out.println("please select a case"); 
    choice = in.nextInt(); 
    if (choice >= cases.size()) { 
     System.out.println("Please select from 0-" + (cases.size() - 1)); 
    } 

} while (choice < cases.size()); 

然後您需要簡單地訪問指定的項目從ArrayList

// Allow for a non-positive exit value... 
if (choice >= 0) { 
    // I know, blind cast, bad idea...keep reading... 
    Case aCase = (Case)cases.get(choice); 
    System.out.println(aCase.getPrice()); 
} 

詳細瞭解Collections。

建議

要注意的是已經有一個在圖書館稱爲Arrays類，它可能是一個好主意，將其重命名刪除混亂。

爲了防止需要從ArrayList投的元素，你應該提供一個通用的返回結果，例如...

相反的public ArrayList Case() {，你應該使用public ArrayList<Case> Case() {，這保證了當你做cases.get，編譯器會預期Case，這意味着你可以做一些像Case case = cases.get(choice);這樣更安全的事情。

在Java中，建議Java方法的名稱以小寫

public ArrayList<Case> case() {... 
public ArrayList<Monitor> monitor() {... 

這也可能是適合使用get的方法來說「得到」的東西，例如...

public ArrayList<Case> getCases() {... 
public ArrayList<Monitor> getMonitors() {...