[Ken Kousen]Modern Java Recipes

1. Example 4-15. Output of summary statistics calculation
   
2. DoubleSummaryStatistics{count=10000, sum=4983.859228, min=0.000264,
   
3. average=0.498386, max=0.999998}
   
4. Other reduction operations like sum, count, max, min, and average do what
   
5. you would expect. The only interesting part is that some of them return
   
6. optionals, because if there are no elements in the stream (perhaps after a
   
7. filtering operation) the result is undefined or null.

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1. Example 4-17. Printing the values of x and y
   
2. int sum = IntStream.rangeClosed(1, 10)
   
3. .reduce((x, y) -> {
   
4. System.out.printf("x=%d, y=%d%n", x, y);
   
5. return x + y;
   
6. }).orElse(0);

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1. Example 4-20. Doubling the values during the sum (WORKS)
   
2. int doubleSum = IntStream.rangeClosed(1, 10)
   
3. .reduce(0, (x, y) -> x + 2 * y);
   
4. // doubleSum == 110 (yay!)
   
5. By providing the initial value of zero for the accumulator x, the value of y is
   
6. assigned to each of the elements in the stream, doubling them all.

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1. Example 5-1. Returning a collection and filtering out nulls
   
2. List<String> strings = Arrays.asList(
   
3. "this", null, "is", "a", null, "list", "of", "strings", null);
   
4. List<String> nonNullStrings = strings.stream()
   
5. .filter(Objects::nonNull)
   
6. .collect(Collectors.toList());

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1. Example 5-2. Testing the filter
   
2. @Test
   
3. public void testNonNulls() throws Exception {
   
4. List<String> strings =
   
5. Arrays.asList("this", "is", "a", "list", "of", "strings");
   
6. assertTrue(Objects.deepEquals(strings, nonNullStrings);
   
7. }

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1. Example 5-3. Filtering nulls from a generic list
   
2. public <T> List<T> getNonNullElements(List<T> list) {
   
3. return list.stream()
   
4. .filter(Objects::nonNull)
   
5. .collect(Collectors.toList());
   
6. }

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1. Example 5-5. Lambda expression for the listener
   
2. String greeting = "Hello, %s!";
   
3. button.addActionListener(e ->
   
4. response.setText(String.format(greeting,name.getText())));

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1. Example 5-6. Sum the values in a List
   
2. List<Integer> nums = Arrays.asList(3, 1, 4, 1, 5, 9);
   
3. int total = 0;
   
4. for (int n : nums) {
   
5. total += n;
   
6. }
   
7. total = 0;
   
8. nums.forEach(n -> total += n);
   
9. total = nums.stream()
   
10. .mapToInt(Integer::valueOf)
    
11. .sum()

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