說明：分別用常規程式碼和Lambda舉例

1. 計算集合空字串數量

   List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd", "", "jkl");
   //1. 常規程式碼
   long count = 0;
   for (String string : strings) {
       if (string.isEmpty()) {
           count++;
       }
   }
   //2. Stream
   count = strings.stream().filter(new Predicate<String>() {
       @Override
       public
    
    boolean test(String s) {
           return s.isEmpty();
       }
   }).count();
   //3. Lambda表示式
   count = strings.stream().filter(String::isEmpty).count();
   //或 count = strings.stream().filter(s->s.isEmpty()).count();
   
   System.out.println("空字串數量為：" + count);//2

2. 計算集合字串長度為3的數量

   List<String> strings = Arrays.asList("abc"
    
   , "", "bc", "efg", "abcd", "", "jkl");
   //1. 常規程式碼
   long count = 0;
   for (String string : strings) {
   
       if (string.length() == 3) {
           count++;
       }
   }
   //2. Stream
   count = strings.stream().filter(new Predicate<String>() {
               @Override
               public boolean test(String s) {
                   return
    
    s.length() == 3;
               }
           }).count();
   //3. Lambda表示式
   count = strings.stream().filter(string -> string.length() == 3).count();
   
   System.out.println("字串長度為 3 的數量為: " + count);//3

3. 刪除集合中的空字串

   List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd", "", "jkl");
   //1. 常規程式碼
   List<String> filtered = new ArrayList<String>();
   for (String string : strings) {
       if (!string.isEmpty()) {
           filtered.add(string);
       }
   }
   //2. Stream
   filtered = strings.stream().filter(new Predicate<String>() {
       @Override
       public boolean test(String s) {
           return !s.isEmpty();
       }
   }).collect(Collectors.toList());
   //3. Lambda表示式
   filtered = strings.stream().filter(s -> !s.isEmpty()).collect(Collectors.toList());
   
   System.out.println("刪除空字串後的列表: " + filtered);//[abc, bc, efg, abcd, jkl]

4. 刪除集合中空字串並使用逗號把它們合併起來

   List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd", "", "jkl");
   //1. 常規程式碼
   StringBuilder sb = new StringBuilder();
   for (String string : strings) {
       if (!string.isEmpty()) {
           sb.append(string);
           sb.append(", ");
       }
   }
   String mergedString = sb.substring(0, sb.length() - 2);
   //2. Stream
   mergedString = strings.stream().filter(new Predicate<String>() {
       @Override
       public boolean test(String s) {
           return !s.isEmpty();
       }
   }).collect(Collectors.joining(", "));
   //3. Lambda表示式
   mergedString = strings.stream().filter(s -> !s.isEmpty()).collect(Collectors.joining(", "));
   
   System.out.println("合併的字串: " + mergedString);//abc, bc, efg, abcd, jkl

5. 獲取集合元素的平方並去重

   List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
   //1. 常規程式碼
   List<Integer> squaresList = new ArrayList<Integer>();
   for (Integer number : numbers) {
       Integer square = number * number;
       if (!squaresList.contains(square)) {
           squaresList.add(square);
       }
   }
   //2. Stream
   squaresList = numbers.stream().map(new Function<Integer, Integer>() {
       @Override
       public Integer apply(Integer i) {
           return i * i;
       }
   }).distinct().collect(Collectors.toList());
   
   //3. Lambda表示式
   squaresList = numbers.stream().map(i -> i * i).distinct().collect(Collectors.toList());
   
   System.out.println("平方數去重列表: " + squaresList);//[9, 4, 49, 25]

6. 求最大最小平均總和等

   List<Integer> integers = Arrays.asList(1, 2, 13, 4, 15, 6, 17, 8, 19);
   
   IntSummaryStatistics stats = integers.stream().mapToInt(new ToIntFunction<Integer>() {
       @Override
       public int applyAsInt(Integer i) {
           return i;
       }
   }).summaryStatistics();
   
   stats = integers.stream().mapToInt(i -> i).summaryStatistics();
   
   System.out.println("集合中最大的數 : " + stats.getMax());//19
   System.out.println("集合中最小的數 : " + stats.getMin());//1
   System.out.println("集合所有數之和 : " + stats.getSum());//85
   System.out.println("集合中的平均數 : " + stats.getAverage());//9.444444444444445

7. 輸出100以內（不包括100）的10個隨機數

   //1. 常規程式碼
   Random random = new Random();
   for (int i = 0; i < 10; i++) {
       System.out.println(random.nextInt(100));
   }
   //2. IntStream
   random.ints(0,100).limit(10).sorted().forEach(new IntConsumer() {
       @Override
       public void accept(int i) {
           System.out.println(i);
       }
   });
   //3. Lambda表示式
   random.ints(0, 100).limit(10).sorted().forEach(System.out::println);

參考