如何打印数组的三种不同类型的对象（可以存储任何类型的对象）并将其打印在单独的数组中？

Question

I have the following codes and I want to modify it so that I can declare three arrays of the same type as objects that I have stored in the ArrayList (for instance arrays of types Integer , Boolean , Double ), scan the ArrayList and each found object to its compatible array. How to do that?

Please help me. Thank you in advance.

package task2;

import java.io.ObjectInputStream;
import java.util.ArrayList;

public class Task2 {

    public static void main(String[] args) {
        ArrayList<Object> something=new ArrayList<Object>();

        //Array elements for integer type
        something.add(10);
        something.add(20);
        something.add(30);
        something.add(40);
        something.add(50);
        something.add(60);

        ////Array elements for boolean type
        something.add("The color of the sky is blue");
        something.add("The color of tree is green");
        something.add("The color of blood is red");
        something.add("The color of termeric is yello ");
        something.add("The color of dark is black");
        something.add("The color of watar is unknown ");

        ////Array elements for double type
        something.add("-10");
        something.add("-20");
        something.add("-30");
        something.add("-40");
        something.add("-50");
        something.add("-60");
        something.add("-70");
        something.add("-80");


        // Type code to print the integer type object
        System.out.println("Your array is with integer object:");

        for(int intcounter=0; intcounter<5;intcounter++)
        {
            System.out.println(something.get(intcounter));
        }

        // Type code to print the boolean type object
        {

        }

        // Type code to print the boolean type object
        {

        }
    }
}

Answer 1

I think that this is what you want:

List integers = new ArrayList<Integer>();
List doubles = new ArrayList<Double>();
List booleans = new ArrayList<Boolean>();

for(Object obj: something){
    if(obj instanceof Integer){
       integers.add(obj)
    }
    else if(obj instanceof Double){
       doubles.add(obj)
    }
    else if(obj instanceof Boolean){
       booleans.add(obj)
    }

}

Answer 2

您可以使用Guava ，例如：

Iterable<Integer> onlyIntegers = Iterables.filter(something, Integer.class);

Answer 3

You can do as follows.. But you need to slightly alter your array inputs.. Because the way you do it, you are adding strings as booleans and doubles, you need to add the actualy primitive type.

    if (obj instanceof Integer) {
         System.out.println("Found Integer:" + obj.toString());
    }
    if (obj instanceof Boolean) {
         System.out.println("Found Boolean:" + obj.toString());
    }
    if (obj instanceof Double) {
         System.out.println("Found Double:" + obj.toString());
    }

I did a solution from your example, hope it makes sense. As you can see the types added for boolean and double are the actual type.

package task2;
import java.io.ObjectInputStream;
import java.util.ArrayList;

public class Task2 {

/**
 * @param args the command line arguments
 */
public static void main(String[] args) {
    ArrayList<Object> something=new ArrayList<Object>();

    //Array elements for integer type
    something.add(10);
    something.add(20);
    something.add(30);
    something.add(40);
    something.add(50);
    something.add(60);

    ////Array elements for boolean type
    something.add(true);
    something.add(false);

    ////Array elements for double type
    something.add(40.1);
    something.add(50.1);
    something.add(60.1);
    something.add(70.1);
    something.add(80.1);


    // Type code to print the integer type object
    System.out.println("Your array is with integer object:");

    for(int i=0; i<something.size();i++){
       Object obj = something.get(i);

       if (obj instanceof Integer) {
          System.out.println("Found Integer:" + obj.toString());
       }
       if (obj instanceof Boolean) {
          System.out.println("Found Bool:" + obj.toString());
       }
       if (obj instanceof Double) {
           System.out.println("Found Double:" + obj.toString());
       }
    }
  }
}