속성으로 ArrayList에서 개체를 찾는 방법

속성으로 ArrayList에서 개체를 찾는 방법

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어떻게 개체를 찾을 수 있습니다 CarnetA의, ArrayList<Carnet>알고 그 특성 codeIsin.

List<Carnet> listCarnet = carnetEJB.findAll();

public class Carnet {

    private String codeTitre;
    private String nomTitre;
    private String codeIsin;

    // Setters and getters

}

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반복 없이는 할 수 없습니다.

옵션 1

Carnet findCarnet(String codeIsIn) {
    for(Carnet carnet : listCarnet) {
        if(carnet.getCodeIsIn().equals(codeIsIn)) {
            return carnet;
        }
    }
    return null;
}

옵션 2

의 equals()메서드를 재정의합니다 Carnet.

옵션 3

당신의 저장 ListA와 Map사용하는 대신 codeIsIn키로 :

HashMap<String, Carnet> carnets = new HashMap<>();
// setting map
Carnet carnet = carnets.get(codeIsIn);

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Java8 에서는 스트림을 사용할 수 있습니다.

public static Carnet findByCodeIsIn(Collection<Carnet> listCarnet, String codeIsIn) {
    return listCarnet.stream().filter(carnet -> codeIsIn.equals(carnet.getCodeIsin())).findFirst().orElse(null);
}

또한 여러 다른 객체 (뿐만 아니라 Carnet)가 있거나 다른 속성으로 찾고자하는 경우 (뿐만 아니라 cideIsin) 유틸리티 클래스를 빌드하여이 논리를 캡슐화 할 수 있습니다.

public final class FindUtils {
    public static <T> T findByProperty(Collection<T> col, Predicate<T> filter) {
        return col.stream().filter(filter).findFirst().orElse(null);
    }
}

public final class CarnetUtils {
    public static Carnet findByCodeTitre(Collection<Carnet> listCarnet, String codeTitre) {
        return FindUtils.findByProperty(listCarnet, carnet -> codeTitre.equals(carnet.getCodeTitre()));
    }

    public static Carnet findByNomTitre(Collection<Carnet> listCarnet, String nomTitre) {
        return FindUtils.findByProperty(listCarnet, carnet -> nomTitre.equals(carnet.getNomTitre()));
    }

    public static Carnet findByCodeIsIn(Collection<Carnet> listCarnet, String codeIsin) {
        return FindUtils.findByProperty(listCarnet, carnet -> codeIsin.equals(carnet.getCodeIsin()));
    }
}

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다음은 Guava를 사용하는 솔루션입니다.

private User findUserByName(List<User> userList, final String name) {
    Optional<User> userOptional =
            FluentIterable.from(userList).firstMatch(new Predicate<User>() {
                @Override
                public boolean apply(@Nullable User input) {
                    return input.getName().equals(name);
                }
            });
    return userOptional.isPresent() ? userOptional.get() : null; // return user if found otherwise return null if user name don't exist in user list
}

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If you use Java 8 and if it is possible that your search returns null, you could try using the Optional class.

To find a carnet:

private final Optional<Carnet> findCarnet(Collection<Carnet> yourList, String codeIsin){
    // This stream will simply return any carnet that matches the filter. It will be wrapped in a Optional object.
    // If no carnets are matched, an "Optional.empty" item will be returned
    return yourList.stream().filter(c -> c.getCodeIsin().equals(codeIsin)).findAny();
}

Now a usage for it:

public void yourMethod(String codeIsin){
    List<Carnet> listCarnet = carnetEJB.findAll();

    Optional<Carnet> carnetFound = findCarnet(listCarnet, codeIsin);

    if(carnetFound.isPresent()){
        // You use this ".get()" method to actually get your carnet from the Optional object
        doSomething(carnetFound.get());
    }
    else{
        doSomethingElse();
    }
}

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Override hashcode and equals methods

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For finding objects which are meaningfully equal, you need to override equals and hashcode methods for the class. You can find a good tutorial here.

http://www.thejavageek.com/2013/06/28/significance-of-equals-and-hashcode/

ReferenceURL : https://stackoverflow.com/questions/17526608/how-to-find-an-object-in-an-arraylist-by-property