如何通过我的静态方法将值传递给我的对象数组 [英] How to pass values to my object array from my static method
问题描述
我有3个类，一个EyMain是我的主类，在其中我读取一个 n值> 100 ，该对象创建我的对象数组的数量。然后调用 writeUSB（）方法在其中填充对象数组。
I have 3 classes one EyMain that is my main class where I read a "n" value > 100 that creates the number of my object arrays.Then I call writeUSB() method where I fill the object array.
public class EyMain {
public static void main(String[] args) {
int n;
do {
System.out.println("Give an integer value > 100 : ");
n = scannerUserInput.getInteger();
} while (n < 101);
ekpaideytikoYliko usb[] = new ekpaideytikoYliko[n];
eYMethods.writeUSB(usb);
eYMethods.showDocs(usb);
}
}
我的另一类是eYMethods我有2个静态方法 writeUSB ，我想返回存储在数组中的最后一个元素的指针，因为我想检查我的 memorySpace> 8gb是否要从中删除数组并更新数组的最后一个元素和 showDocs ，我只希望打印用户键入的对象数组中的元素，而只打印带有的文件扩展名。 doc或.docx 。
My other class is eYMethods where I have my 2 static methods writeUSB that I want to return the pointer of the last element that have stored in my array because I want to check if my memorySpace > 8gb I want to remove it from the array and updating the last element of the array and showDocs that I want to print only the elements from the object array that the user has typed and print only the file extension with .doc or .docx .
package eymain;
public class eYMethods {
static double writeUSB(ekpaideytikoYliko usb[]) {
for(int i = 0; i < usb.length; i++) {
System.out.println("Give fileName : ");
usb[i].setFileName(scannerUserInput.getString());
System.out.println("Give minutes : ");
usb[i].setMinutes(scannerUserInput.getDouble());
System.out.println("Give memorySpace");
usb[i].setMemorySpace(scannerUserInput.getDouble());
}
return 0;
}
static void showDocs(ekpaideytikoYliko usb[]) {
for(int i =0; i < usb.length; i++) {
System.out.println("fileName : " + usb[i].getFileName());
System.out.println("minutes : " + usb[i].getMinutes());
System.out.println("memorySpace : " + usb[i].getMemorySpace());
}
}}
最后一堂课是我的ekapideytikoYliko私有变量，get和set，我的构造函数和一个String方法getFileType，我想从fileName中获取扩展名。例子（.doc，.docx，.mp4）。
And last class is my ekapideytikoYliko that I have my private variables, get and set, my constructor and a String method getFileType that I want to take from the fileName the extension from it. Example(.doc, .docx, .mp4).
package eymain;
public class ekpaideytikoYliko {
private String fileName;
private double minutes;
private double memorySpace;
ekpaideytikoYliko(String fileName, double minutes, double memorySpace) {
this.fileName = fileName;
this.minutes = minutes;
this.memorySpace = memorySpace;
}
public String getFileName() {
return fileName;
}
public void setFileName(String fileName) {
this.fileName = fileName;
}
public double getMinutes() {
return minutes;
}
public void setMinutes(double minutes) {
this.minutes = minutes;
}
public double getMemorySpace() {
return memorySpace;
}
public void setMemorySpace(double memorySpace) {
this.memorySpace = memorySpace;
}
String getfileType(ekpaideytikoYliko usb[]) {
int name = fileName.lastIndexOf(".");
if (name == -1) {
return "";
}
return fileName.substring(name);
}}
还有我的scannerUserInput文件：
And my scannerUserInput file :
package eymain;
import java.util.Scanner;
public class scannerUserInput {
static int getInteger(){
Scanner ob = new Scanner(System.in);
try{
int i = ob.nextInt();
return i;
}
catch(Exception e){
return -1;
}
}
static byte getByte(){
Scanner ob = new Scanner(System.in);
try{
byte b = ob.nextByte();
return b;
}
catch(Exception e){
return -1;
}
}
static short getShort(){
Scanner ob = new Scanner(System.in);
try{
short s = ob.nextShort();
return s;
}
catch(Exception e){
return -1;
}
}
static long getLongInteger(){
Scanner ob = new Scanner(System.in);
try{
long l = ob.nextLong();
return l;
}
catch(Exception e){
return -1;
}
}
static float getFloat(){
Scanner ob = new Scanner(System.in);
try{
float f = ob.nextFloat();
return f;
}
catch(Exception e){
return -1;
}
}
static double getDouble(){
Scanner ob = new Scanner(System.in);
try{
double d = ob.nextDouble();
return d;
}
catch(Exception e){
return -1;
}
}
static String getString(){
Scanner ob = new Scanner(System.in);
try{
String s = ob.nextLine();
return s;
}
catch(Exception e){
return "";
}
}
static char getChar(){
Scanner ob = new Scanner(System.in);
try{
char ch = ob.next().charAt(0);
return ch;
}
catch(Exception e){
return ' ';
}
}
}
当我在 writeUSB 方法中键入来自扫描仪的数据，我的第一种类型出现错误。
When I type inside the writeUSB method the data from the scanner I get an error in my first type.
推荐答案
在Java中，如果根据情况创建对象数组，则为：
In java when you create an array of an object in your case it is:
ekpaideytikoYliko usb[] = new ekpaideytikoYliko[n];
Java只是这样做
// Lets say n = 5 for easier demonstration
{null, null, null, null, null}
来源：变量的初始值
对于所有引用类型（第4.3节），默认值为
For all reference types (§4.3), the default value is null.
现在在 eYMethods 中尝试调用方法时只返回nullpointer，因为该元素为null。要解决此问题，您需要创建一个对象并将该对象存储在数组中。像这样的东西：
Now when in eYMethods when you try do call a method it just return nullpointer because that element is null. To fix that you need to create an object and store that object in array. Something like this:
for (int i = 0; i < usb.length; i++) {
System.out.println("Give fileName : ");
String fileName = scannerUserInput.getString();
System.out.println("Give minutes : ");
double minutes = scannerUserInput.getDouble();
System.out.println("Give memorySpace");
double memorySpace = scannerUserInput.getDouble();
ekpaideytikoYliko tempEkpaideytikoYliko = new ekpaideytikoYliko(fileName, minutes, memorySpace);
usb[i] = tempEkpaideytikoYliko;
}
现在，java将创建一个 ekpaideytikoYliko 并将其存储在数组中。
Now java will create an Object of Class ekpaideytikoYliko and store it in array.
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