我在这里发布了两个类（以及从中创建对象的计算机类）。
当我尝试使用自己的findSys方法时，无论如何，我的方法都将返回“ null”。我正在尝试将用户作为findSys参数输入的“搜索”变量与null进行比较，如果为null，则应在“ else”子句下输出我收到的消息。但是，无论如何，它只是返回null。卡在这里。
import java.util.Scanner;
public class SystemTester {
public static void main(String args[]) {
Scanner scan = new Scanner(System.in);
String search;
ComputerStore cpu1 = new ComputerStore();
cpu1.add("Pentium II", 32, "2080", "Asus 370", "Corsair", 5, 123, 5);
cpu1.add("Pentium I", 16, "Nvidia 1080", "Asus 270", "CoolerMaster1", 5, 123, 5);
cpu1.add("Pentium III", 4, "GTX 1060", "Gigabyte", "Corssair 2", 5, 123, 5);
cpu1.add("AMD", 4, "GTX 980", "Gigabyte", "Corssair 2", 5, 123, 5);
cpu1.add("AMD Ryzen", 4, "GTX 680", "Gigabyte", "Corssair 2", 5, 123, 5);
cpu1.add("Core I5", 4, "GTX 1080ti", "Gigabyte", "Corssair 2", 5, 123, 5);
cpu1.add("Core I7", 4, "GTX 1060 SLI", "Gigabyte", "Corssair 2", 5, 123, 5);
cpu1.add("Core I9", 4, "GTX 780", "Gigabyte", "Corssair 2", 5, 123, 5);
cpu1.add("AMD Ryzen 2", 4, "Voodoo2", "Gigabyte", "Corssair 2", 5, 123, 5);
cpu1.add("I7 5820k", 4, "Voodoo1", "Gigabyte", "Corssair 2", 5, 123, 5);
ComputerStore cpu2 = new ComputerStore();
cpu2.add("Haswell", 64, "Nvidia 1080", "Aztek", "Corsair", 3.5, 455, 5.5);
System.out.println("Please enter a CPU to search for (Press q to quit)");
search = scan.nextLine();
while (!"q".equals(search)) {
if (search != null) {
System.out.println(cpu1.findSys(search));
}
else {
if (search.equals(null))
System.out.println("test");
}
System.out.println("Please enter a CPU to search for (Press q to quit)");
search = scan.nextLine();
}
}
}
public class ComputerStore {
private Computer[] systems;
private int sysNumbers;
public ComputerStore() {
systems = new Computer[200];
sysNumbers = 0;
}
public void add(String c, int r, String g, String m, String p, double co, int sn, double d) {
systems[sysNumbers++] = new Computer(c, r, g, m, p, co, sn, d);
}
public String toString() {
String result = "";
for (int i = 0; i < sysNumbers; i++)
result += systems[i].toString() + "\n";
return result;
}
public String findSys(String c) {
for (int i = 0; i < sysNumbers; i++) {
if (systems[i] != null && systems[i].getCpu().equals(c))
return systems[i].getMotherboard();
}
return null;
}
}
//
//This program will create Computer objects with different data members
//and will also upgrade those data members based on setters. This program
//also has a depreciation function and upgrade function. This (Computer) is the class
//and the SystemBuilder class is the class used for creating the objects.
public class Computer {
// Data Members - These belong to the class and are private.
// They all go to new objects.
private String cpu;
private int ram;
private String gpu;
private String motherboard;
private String psu;
private double cost;
private int serialnumber;
private double depreciation;
// Initial constructor with no arguments
Computer() {
cpu = "";
ram = 0;
gpu = "";
motherboard = "";
psu = "";
cost = 0.0;
serialnumber = 0;
depreciation = 0.0;
}
// Constructor with data members
Computer(String c, int r, String g, String m, String p, double co, int sn, double d) {
cpu = new String(c);
ram = r;
gpu = new String(g);
motherboard = new String(m);
psu = new String(p);
cost = co;
serialnumber = sn;
depreciation = d;
}
// Getters, allow retrieval of data members from outside of class
public String getCpu() {
return cpu;
}
public int getRam() {
return ram;
}
public String getGpu() {
return gpu;
}
public String getMotherboard() {
return motherboard;
}
public String getPsu() {
return psu;
}
public double getCost() {
return cost;
}
public int getSerialnumber() {
return serialnumber;
}
public double getDepreciation() {
return depreciation;
}
// Setters, allow setting of data members from outside of class
public void setCpu(String c) {
cpu = new String(c);
}
public void setRam(int r) {
ram = r;
}
public void setGpu(String g) {
gpu = new String(g);
}
public void setMotherboard(String m) {
motherboard = new String(m);
}
public void setPsu(String p) {
psu = new String(p);
}
public void setCost(double co) {
cost = co;
}
public void setSerialnumber(int sn) {
serialnumber = sn;
}
public void setDepreciation(double d) {
depreciation = d;
}
// Boolean below will compare computers to see if equal
// based on same motherboard SN#.
public boolean equals(Computer c) {
if (this.serialnumber == (c.serialnumber)) {
return true;
} else {
return false;
}
}
// To string method will print characteristics about object.
public String toString() {
return ("CPU:\t\t" + cpu + "\n" + "RAM:\t\t" + ram + "\n" + "GPU:\t\t" + gpu + "\n" + "Motherboard:\t"
+ motherboard + "\n" + "PSU:\t\t" + psu + "\n" + "Cost:\t\t" + "$" + cost + "\n" + "SN#:\t\t"
+ serialnumber + "\n" + "Depreciation:\t" + "$" + depreciation + " (annually)");
}
// A method to depreciate the cost of the computer
// The formula is observed below, but this is a
// straight line depreciation equation, calculated based
// on the values the user passes into the function. This method
// will show an output of annual depreciation based on useful
// life, entered in "years" by the user.
public void depreciate(double purchasePrice, double salvageValue, double lifeSpanYears) {
double depreciableCost;
double annualDepreciation;
depreciableCost = purchasePrice - salvageValue;
annualDepreciation = depreciableCost / lifeSpanYears;
depreciation = annualDepreciation;
}
// A method to upgrade the ram or the video card
// The method will accpet argumetns for ram (in int) and a gpu (string).
public void upgrade(int newRam, String newGpu) {
ram = newRam;
gpu = new String(newGpu);
}
}
答案 0 :(得分：0)
对我来说，您的实现是完美的。这里附上了屏幕截图，可能是您在输入输入搜索文本时在控制台输入过程中做错了。Console out put snapshot
答案 1 :(得分：0)
您不想比较search == null是否为search是用户输入。您要检查搜索结果是否为null：
while (!"q".equals(search)) {
Computer searchResult = cpu1.findSys(search);
if (searchResult != null) {
System.out.println(searchResult);
}
else {
System.out.println("not found");
}
您还应该将findSys的返回类型更改为Computer。仅返回String会限制该函数的用途：
public Computer findSys(String c) {
for (int i = 0; i < sysNumbers; i++) {
if (systems[i] != null && systems[i].getCpu().equals(c))
return systems[i];
}
return null;
}
答案 2 :(得分：0)
好吧
先生。 Mopp是正确的-但我必须在searchResult变量之前删除Computer类，然后才能使它工作，并创建String的var类型SearchResult。因此，这在下面对我有用：
String searchResult;
while (!"q".equals(search)) {
searchResult = cpu1.findSys(search);
if (searchResult != null) {
System.out.println(searchResult);
}
else {
System.out.println("not found");
}