Java 8 Lambdas Pass函數或變量作爲參數

Question

我是Java 8 lambda的新手。我有一個代碼開頭：

StringBuilder lemma = new StringBuilder("("); 

和比兩塊代碼。第一招：

lemma.append("("); 

for (String dt : dts) { 
    lemma.append("label1:").append(labelList.getLabel1(dt)).append(OPERATOR); 
} 

lemma.delete(lemma.length() - OPERATOR.length(), lemma.length()); 
lemma.append(")"); 

第二個：

lemma.append("("); 

for (String mt : mts) { 
    lemma.append("label2:").append(mt).append(OPERATOR); 
} 

lemma.delete(lemma.length() - OPERATOR.length(), lemma.length()); 
lemma.append(")"); 

我怎樣才能使其中涵蓋了功能2件代碼接受參數：

List<String> (which is for -dts- or -mts-) 

和

String (which is for -"label1:"- or -"label2:"-) 

and

func() (which is for -labelList.getLabel1(dt)- or -mt-) 

是否有可能用Java 8 lambda做這樣的事情？

Answer 1

你可以把它寫這樣

public static <T> String dump(List<T> list, String desc, Function<T, String> func) { 
    StringBuilder lemma = new StringBuilder(); 
    String sep = "("; 
    for (T t : list) { 
     lemma.append(sep).append(desc).append(func.apply(t)); 
     sep = OPERATOR; 
    } 
    return lemma.length() == 0 ? "()" : lemma.append(")").toString(); 
} 

您可以通過

String a = dump(dts, "cuzco:", huancayo::getCuzco); 
String b = dump(mts, "cucuta:", m -> m); 

Answer 2

使用流和StringJoiner/Collectors.joining（和調整彼得斯接受的答案）調用這些：

public static <T> String dump(String label, List<T> list, Function<T, String> func) { 
    return list.stream() 
      .map(s -> label + func.apply(s)) 
      .collect(Collectors.joining(OPERATOR, "(", ")")); 
} 

該呼叫將是相同的：

String a = dump(dts, "label1:", labelList::getLabel1); 
String b = dump(mts, "label2:", m -> m); 
// or: dump(mts, "label2:", Function.identity())