java - 使用 Java 8 Lambda 表达式查找票据列表是否具有不同货币

Question

我有一张纸币列表，每张纸币都有特定的货币。如果所有纸币的货币都相同，我想退回货币。如果其中任何一张纸币具有不同的货币，则抛出异常。如何使用 Java 8 lambda 表达式来实现这一点？

    public class Money {
        private List<NoteTO> notes;

        public List<NoteTO> getNotes() {
            return notes;
        }

        public void setNotes(List<NoteTO> notes) {
            this.notes = notes;
        }
    }

    public class NoteTO {
        private Long noteId;
        private String currency;

        public Long getNoteId() {
            return noteId;
        }

        public void setNoteId(Long noteId) {
            this.noteId = noteId;
        }

        public String getCurrency() {
            return currency;
        }

        public void setCurrency(String currency) {
            this.currency = currency;
        }
    }

我通过以下方式实现了这一点。但是，想要使用 Lambda 表达式执行相同的操作。

    public void testMethod(){
        String currencyResponse = null;
        for(NoteTO note : notes){
            currencyResponse = checkCurrency(currencyResponse, note);
        }

        System.out.println("Currency : "+currencyResponse);
    }

    public String checkCurrency(String currencyResponse, NoteTO note) throws Exception {
        String currency = note.getCurrency();

        if(currencyResponse == null){
            return currency;
        } else if(!currencyResponse.equals(currency)){
            throw new Exception();
        }

        return currencyResponse;
    }

Answer 1

您可以使用Stream::allMatch .

List<Note> notes = ...;

String currency = notes.isEmpty() ? null : notes.get(0).getCurrency();
if(!notes.stream().allMatch(e -> currency.equals(e.getCurrency())))
    throw new Exception();

System.out.println("Currency : " + currency);

请注意，您不能从 lambda 引发异常(在本例中)。所以你必须为此进行单独的检查。