Searching in a ArrayList with custom objects for certain strings

Question

I have a ArrayList with custom objects. I want to search inside this ArrayList for Strings.

The class for the objects look like this:

public class Datapoint implements Serializable {

  private String stateBased;
  private String name;
  private String priority;
  private String mainNumber;
  private String groupadress;
  private String dptID;

  public Datapoint(){
  }

  public String getMainNumber() {
    return mainNumber;
  }

  public void setMainNumber(String mainNumber) {
    this.mainNumber = mainNumber;
  }

  public String getName() {
    return name;
  }

  ..and so on

I know how to search for a string in a ArrayList but how to do that in a ArrayList with my custom objects:

ArrayList<String> searchList = new ArrayList<String>();
String search = "a";
int searchListLength = searchList.size();
for (int i = 0; i < searchListLength; i++) {
if (searchList.get(i).contains(search)) {
//Do whatever you want here
}
}

So I want to have a function to search in my ArrayList with for example five objects for all "name" strings.

Answer 1

The easy way is to make a for where you verify if the atrrtibute name of the custom object have the desired string

    for(Datapoint d : dataPointList){
        if(d.getName() != null && d.getName().contains(search))
           //something here
    }

I think this helps you.

Answer 2

UPDATE: Using Java 8 Syntax

List<DataPoint> myList = new ArrayList<>();
//Fill up myList with your Data Points

List<DataPoint> dataPointsCalledJohn = 
    myList
    .stream()
    .filter(p-> p.getName().equals(("john")))
    .collect(Collectors.toList());

If you don't mind using an external libaray - you can use Predicates from the Google Guava library as follows:

class DataPoint {
    String name;

    String getName() { return name; }
}

Predicate<DataPoint> nameEqualsTo(final String name) {
    return new Predicate<DataPoint>() {

        public boolean apply(DataPoint dataPoint) {
            return dataPoint.getName().equals(name);
        }
    };
}

public void main(String[] args) throws Exception {

    List<DataPoint> myList = new ArrayList<DataPoint>();
    //Fill up myList with your Data Points

    Collection<DataPoint> dataPointsCalledJohn =
            Collections2.filter(myList, nameEqualsTo("john"));

}

Answer 3

try this

ArrayList<Datapoint > searchList = new ArrayList<Datapoint >();
String search = "a";
int searchListLength = searchList.size();
for (int i = 0; i < searchListLength; i++) {
if (searchList.get(i).getName().contains(search)) {
//Do whatever you want here
}
}

Answer 4

Probably something like:

ArrayList<DataPoint> myList = new ArrayList<DataPoint>();
//Fill up myList with your Data Points

//Traversal
for(DataPoint myPoint : myList) {
    if(myPoint.getName() != null && myPoint.getName().equals("Michael Hoffmann")) {
        //Process data do whatever you want
        System.out.println("Found it!");
     }
}

Answer 5

For a custom class to work properly in collections you'll have to implement/override the equals() methods of the class. For sorting also override compareTo().

See this article or google about how to implement those methods properly.

Answer 6

contains() method just calls equals() on ArrayList elements, so you can overload your class's equals() based on the name class variable. Return true from equals() if name is equal to the matching String. Hope this helps.

Answer 7

Use Apache CollectionUtils:

CollectionUtils.find(myList, new Predicate() {
   public boolean evaluate(Object o) {
      return name.equals(((MyClass) o).getName());
   }
}

Answer 8

String string;
for (Datapoint d : dataPointList) {    
   Field[] fields = d.getFields();
   for (Field f : fields) {
      String value = (String) g.get(d);
      if (value.equals(string)) {
         //Do your stuff
      }    
   }
}

Answer 9

boolean found;

for(CustomObject obj : ArrayOfCustObj) {

   if(obj.getName.equals("Android")) {

      found = true;
   }
}