How to filter ArrayList by using multi member variable condition?

Question

I'd like to get objects of DataObj which age greater than 32 and address is city2.
How to filter like this?

Following is tried code.

package com.company;

import java.util.ArrayList;

public class Main {
    public static void main(String[] args) {

        ArrayList<DataObj> arr_datalist = new ArrayList<DataObj>();
        ArrayList<DataObj> arr_filteredlist;
        arr_datalist.add(new DataObj(1, "aka", 30, "city1"));
        arr_datalist.add(new DataObj(2, "akb", 31, "city2"));
        arr_datalist.add(new DataObj(3, "akc", 32, "city2"));
        arr_datalist.add(new DataObj(4, "akd", 33, "city1"));
        arr_datalist.add(new DataObj(5, "ake", 34, "city3"));

        // age greater than 32 and address is city2.
        arr_filteredlist = arr_datalist.filter(???);

    }
}

class DataObj {
    int i_id;
    String str_name;
    int i_age;
    String str_address;

    DataObj(int id, String name, int age, String address) {
        this.i_id = id;
        this.str_name = name;
        this.i_age = age;
        this.str_address = address;
    }
}

Look at this post, can be useful stackoverflow.com/questions/9146224/arraylist-filter — bary
– bary, Commented Dec 4, 2013 at 12:14

Jean Logeart · Accepted Answer · 2013-12-04 12:22:06Z

5

You have several common options:

Do it yourself:

List<DataObj> arr_filteredlist = new ArrayList<>();
for(DataObj e : arr_datalist) {
    if(e.i_age > 32 && e.str_address.equals("city2")) {
        arr_filteredlist.add(e);
    }
}

Guava:

Collection<DataObj> filteredColl = Collections2.filter(arr_datalist,
    new Predicate<DataObj>() {
        @Override
        boolean apply(DataObj e) {
            return e.i_age > 32 && e.str_address.equals("city2");
        }
        // + overrides equals
    });
List<DataObj> arr_filteredlist = new ArrayList<>(filteredColl);

Java 8:

List<DataObj> arr_filteredlist = 
    arr_datalist.stream()
                .filter(e-> e.i_age > 32 && e.str_address.equals("city2"))
                .collect(Collectors.toList());

answered Dec 4, 2013 at 12:22

Jean Logeart

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1 Comment

S.J. Lim Over a year ago

solution of each version. :D Thank you for your answer.

Silviu Burcea · Accepted Answer · 2013-12-04 12:15:59Z

4

Starting with Java 8, we will have lambdas. Your task can be solved by:

List<DataObj> filteredList = arr_datalist.stream()
                              .filter(dataObj -> dataObj.str_address.equals("city2") && dataObj.i_age > 32)
                              .map(DataObj::new)
                              .collect(Collectors.toList());

answered Dec 4, 2013 at 12:15

Silviu Burcea

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1 Comment

Silviu Burcea Over a year ago

@S.J.Lim Yes, can't wait for General Availability. You can download an early release too: jdk8.java.net/download.html

eebbesen · Accepted Answer · 2013-12-04 12:16:49Z

0

ArrayList<DataObj> filteredList = new ArrayList<DataObj>();
for (DataObj dataObj : arr_datalist) {
    if (32 < dataObj.getAge()  && "city2".equals(dataObj.getCity()) {
        filteredList.add();
    }
}

answered Dec 4, 2013 at 12:16

eebbesen

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Comments

Philipp Sander · Accepted Answer · 2013-12-04 12:17:22Z

There is no filter mechanism in java7 or previous versions. but you can easily do this yourself by checking each object:

    ArrayList<DataObj> arr_datalist = new ArrayList<DataObj>();
    ArrayList<DataObj> arr_filteredlist = new ArrayList<DataObj>();
    arr_datalist.add(new DataObj(1, "aka", 30, "city1"));
    arr_datalist.add(new DataObj(2, "akb", 31, "city2"));
    arr_datalist.add(new DataObj(3, "akc", 32, "city2"));
    arr_datalist.add(new DataObj(4, "akd", 33, "city1"));
    arr_datalist.add(new DataObj(5, "ake", 34, "city3"));

    // age greater than 32 and address is city2.
    for(DataObj obj : datalist) {
        if(obj.getAge() > 32 && "city2".equals(obj.getAddress()) {
            filteredlist .add(obj);
        }
    }

I assmue your DataObj has private attributes and a getter for each attribute.

Santosh Joshi · Accepted Answer · 2013-12-04 12:28:39Z

0

Define a predicate

Predicate<DataObj> filterPredicate = new Predicate<DataObj>() {
   public boolean apply(DataObj obj) {
    if(obj.getAge() > 32 && obj.getAddress.equals("city2") {
       return true;
    }
    return false;
}

Define your generic function

public static <T> Collection<T> filter(Collection<T> source, Predicate<T> predicate) {
    Collection<T> result = new ArrayList<T>();
    for (T element: source) {
       if (predicate.apply(element)) {
          result.add(element);
      }
    }
   return result;
 }

Call It

 Collection<DataObj> filteredObjects = filter(arr_datalist, filterPredicate);

answered Dec 4, 2013 at 12:28

Santosh Joshi

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2 Comments

Silviu Burcea Over a year ago

Note: you need Guava :)

Santosh Joshi Over a year ago

@SilviuBurcea, no need to use guava in this case as you can create your Predicate class with apply method

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