[英]Avoid type casting
我有一個稱為Data
的空接口,該接口由DataOne
和DataTwo
類實現。
然后,我有一個名為DataHolder
的類,其中包含一個Data
對象。
看起來像這樣:
public class DataHolder() {
public Data data;
}
public class DataOne() {
public int importantData;
public int getImportantData() {
return importantData;
}
public int setImportantData(int importantData) {
this.importantData = importantData;
}
}
public class DataTwo() {
public int notSoImportantData;
}
假設有一個函數接受DataHolder
對象並對重要數據整數進行一些操作。
public void calculateImportantData(DataHolder dh) {
int importantData = 1234567890;
dh.data.setImportantData(importantData);
}
我如何確定DataHolder
包含一個DataOne
對象,而不進行類型轉換?
怎么樣:
public class DataHolder<T extends Data> {
public T data;
}
在您的代碼中,您將擁有:
public void calculateImportantData(DataHolder<DataOne> dh) {
int importantData = 1234567890;
dh.data.setImportantData(importantData);
}
我假設您的意思是DataOne和DataTwo實現數據。
首先,我對您的代碼進行了一些調整,
1-我創建了一個接口Data,其中包含一些隨機方法someMethod():
package main.interfaces;
public interface Data {
int myData = 0;
public void someMethod();
}
2-然后,我創建了兩個名為DataOne和DataTwo的類:DataOne類:(請注意,我在這里如何添加重要的業務方法setImportantData(),這提供了您工作的全部封裝 )。
package main;
import main.interfaces.Data;
public class DataOne implements Data{
public int importantData;
public int getImportantData() {
return importantData;
}
public void setImportantData(int importantData) {
this.importantData = importantData;
}
@Override
public void someMethod() {
System.out.println("here in DataOne!... ");
}
public void calculateImportantData(int importantData) {
// int importantData = 1234567890;
setImportantData(importantData);
}
}
類數據二:
package main;
import main.interfaces.Data;
public class DataTwo implements Data{
public int notSoImportantData;
@Override
public void someMethod() {
System.out.println("here in DataTwo!...");
}
public void calculateUsualData(DataTwo d2) {
d2.someMethod();
}
}
之后,使用Factory Design Pattern ...創建了這個DataFactory類:
package main.factory;
import main.DataOne;
import main.DataTwo;
import main.interfaces.Data;
public class DataFactory {
public static Data getData(String dataType){
if(dataType == null){
return null;
}
if(dataType.equalsIgnoreCase("DATAONE")){
return new DataOne();
} else if(dataType.equalsIgnoreCase("DATATWO")){
return new DataTwo();
}
return null;
}
}
現在,回到您的問題解決方案中,我使用了DataHolder,將DataFactory封裝在這里:
package main.holder;
import main.factory.DataFactory;
import main.interfaces.Data;
public class DataHolder {
Data data;
public DataHolder(String dataType){
data = DataFactory.getData(dataType);
}
public Data getData(){
return data;
}
}
現在,嘗試運行該應用程序,我添加了一些注釋,這些注釋將出現在您的控制台上,希望對您有所幫助:)
package main.run;
import main.DataOne;
import main.DataTwo;
import main.holder.DataHolder;
import main.interfaces.Data;
public class main {
public static void main(String[] args) {
// lets assume user of the method passed a DataOne Object, you can
// manage it by changing the value of flag string
String flag = "DataOne";
DataHolder dataHolder = new DataHolder(flag);
if (dataHolder.getData() instanceof DataOne) {
System.out
.println("you have a DataOne object , but a Data reference");
System.out
.println("/nso , you need to create a 'reference' to DataOne to work on that object ...");
} else if (dataHolder.getData() instanceof DataTwo) {
System.out
.println("you have a DataTwo object , but a Data reference");
} else {
System.out
.println("you dont have a DataOne nor DataTwo references , it is a "
+ dataHolder.getData().getClass() + " object!");
}
System.out
.println("in order for the compiler to pass the following test , you must cast he RHS ( right hand side ) to match the LHS (left hand side)");
// in order for the compiler to pass the following test , you must cast
// the RHS ( right hand side ) to match the LHS (left hand side)
DataOne d1 = (DataOne) dataHolder.getData();
// in case you wanted to test DataTwo scenario
//DataTwo d2 = (DataTwo) dataHolder.getData();
System.out.println("if you didnt do that , you can make it a Data Object , but you will not be able to access the method 'getImportantData()' created in DataOne");
Data data = dataHolder.getData();
}
}
(請注意,這里的程序結構是:在啟動應用程序之前,選擇數據的類型,將其存儲在main方法中的“ flag”變量中。此后,將調用DataHolder方法,之后,您將可以檢查返回的對象並檢查它是否是您先前指定的對象。如果您希望它有點復雜,可以在DataHolder的構造函數中傳遞對象類型,然后從那里進行檢查,我不想這樣做只是為了簡單起見。祝您好運)
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