Exception : java.util.LinkedHashMap cannot be cast to com.excel.entity.ClassA - mysql

Question

This is the generic method through which i am accepting list of
objects and downcasting to a specific object
public Response generate(List<?> list){
List<ClassA> List1 = new ArrayList<ClassA>();
List<ClassB> List2 = new ArrayList<ClassB>();
List<ClassC> List3 = new ArrayList<ClassC>();
if(list instanceof List<?>){
List1=(List<ClassA>) list;//in this line i am getting error
addDataToExcel(List1);
}
else if(list instanceof List<?>){
List2=(List<ClassB>) list;
addDataToExcel(List1);
}
else if(list instanceof List<?>){
List3=(List<ClassC>) list;
addDataToExcel(List1);
}
This is classA
import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Lob;
import javax.persistence.Table;
#Entity
#Table(name="ClassA")
public class ClassA {
#Id
#Column(name="rollNo")
private int rollNo;
#Column(name="name")
private String name;
#Column(name="english")
private double english;
#Column(name="maths")
private double maths;
#Column(name="science")
private double science;
#Column(name="totalMarks")
private double totalMarks;
#Column(name="percentage")
private double percentage;
#Column(name="status")
private boolean status;
#Lob
#Column(name="file", columnDefinition="BLOB")
private byte[] file;
public ClassA() {
// TODO Auto-generated constructor stub
}
public ClassA(int rollNo, String name, double english, double maths, double science, double totalMarks,
double percentage, boolean status, byte[] file) {
super();
this.rollNo = rollNo;
this.name = name;
this.english = english;
this.maths = maths;
this.science = science;
this.totalMarks = totalMarks;
this.percentage = percentage;
this.status = status;
this.file = file;
}
public int getRollNo() {
return rollNo;
}
public void setRollNo(int rollNo) {
this.rollNo = rollNo;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public double getEnglish() {
return english;
}
public void setEnglish(double english) {
this.english = english;
}
public double getMaths() {
return maths;
}
public void setMaths(double maths) {
this.maths = maths;
}
public double getScience() {
return science;
}
public void setScience(double science) {
this.science = science;
}
public double getTotalMarks() {
return totalMarks;
}
public void setTotalMarks(double totalMarks) {
this.totalMarks = totalMarks;
}
public double getPercentage() {
return percentage;
}
public void setPercentage(double percentage) {
this.percentage = percentage;
}
public boolean isStatus() {
return status;
}
public void setStatus(boolean status) {
this.status = status;
}
public byte[] getFile() {
return file;
}
public void setFile(byte[] file) {
this.file = file;
}
}
This is the method which accepts List and generate excel
public void add(List<ClassA> classA) {
System.out.println("entering add");
String excelFilePath = "D:/eclipse_neon/StudentInfo.xlsx";
try {
FileInputStream inputStream = new FileInputStream(new File(excelFilePath));
Workbook workbook = WorkbookFactory.create(inputStream);
Sheet sheet = workbook.getSheetAt(0);
int rowNum = 1;
int a=2;
for(ClassA info: classA){
System.out.println("netering loop");
Row row = sheet.getRow(rowNum++);
row.createCell(2).setCellValue(info.getEnglish());
row.createCell(3).setCellValue(info.getMaths());
row.createCell(4).setCellValue(info.getScience());
row.createCell(5).setCellFormula("SUM(C"+a+","+"D"+a+","+"E"+a+")");
row.createCell(6).setCellFormula("("+"F"+a+"*"+"100"+")"+"/"+"300");
row.createCell(7).setCellValue(info.isStatus());
a++;
}
System.out.println("after for loop");
inputStream.close();
FileOutputStream outputStream = new FileOutputStream("D:/eclipse_neon/StudentInfo.xlsx");
workbook.write(outputStream);
workbook.close();
outputStream.close();
} catch (IOException | EncryptedDocumentException
| InvalidFormatException ex) {
ex.printStackTrace();
}
}
I am not able to downcast to my specific List of class from generic list soo any suggestions are welcomed Thankyou

Answer 1

That's probably because you're sending a list as parameter containing a List and class A is not related to LinkedHashMap (not a subclass for example) and therefore it cannot cast. If you can provide more details what is class A and what is the list you're sending as arguments to your method.
Check https://www.baeldung.com/java-type-casting