Question

JAVA - Given two List objects (input and output), write a generic method that 1) clears output list if it contains any element, and 2) copies every element of input list to the output list in the same order and position. Note that the type of output list can be any super type of the input list (e.g. type(output)=Numeric & type(input)=Double).

import java.util.List;
import java.util.ArrayList;

public class Collections {

   // Modify method signature if needed & implement the body of method
   public static void copy(List output, List input) {
   }

}

RUN THIS TO CHECK CORRECTNESS

import java.util.ArrayList;
import java.util.List;

public class QA4Test {

   // Test code, do not modify
   public static void main(String[] args) {

      List<Number> output = new ArrayList<Number>();
      List<Integer> input = new ArrayList<Integer>();
      input.add(5);
      input.add(3);
      Collections.copy(output, input);
      System.out.println(output.get(0));  // this should be 5

      List<Integer> output3 = new ArrayList<Integer>();
      List<Integer> input3 = new ArrayList<Integer>();
      input3.add(3);
      input3.add(1);
      input3.add(2);
      Collections.copy(output3, input3);
      System.out.println(output3.get(0));  // this should be 3

      List<String> output2 = new ArrayList<String>();
      List<Long> input2 = new ArrayList<Long>();

      // Collections.copy(output2, input2); // will raise error
   }
   
}

Answer 1

import java.util.List;
import java.util.ArrayList;

public class Collections {

    // Modify method signature if needed & implement the body of method
    public static void copy(List output, List input) {
        output.clear();
        for (int i = 0; i < input.size(); i++) {
            output.add(input.get(i));
        }
    }

}