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JJUG Project Lambda Hands-on Materials - Sample Answers
import java.util.ArrayList;
import java.util.List;
public class FizzBuzzWLambda {
private static final String FIZZBUZZ = "FizzBuzz";
private static final String FIZZ = "Fizz";
private static final String BUZZ = "Buzz";
public FizzBuzzWLambda() {
List<Integer> numbers = initNumbers();
numbers.forEach(e -> {
if (e%15 == 0) {
System.out.println(FIZZBUZZ);
} else if (e%3 == 0) {
System.out.println(FIZZ);
} else if (e%5 == 0) {
System.out.println(BUZZ);
} else {
System.out.println(e);
}
});
}
private List<Integer> initNumbers() {
List<Integer> numbers = new ArrayList<>();
for (int i = 0; i <= 100; i++) {
numbers.add(i);
}
return numbers;
}
public static void main(String... args) {
new FizzBuzzWLambda();
}
}
import java.util.LinkedList;
import java.util.List;
import java.util.functions.Mapper;
public class NumberAdder {
Mapper<List<Integer>, Integer> mapper;
public NumberAdder() {
List<Integer> numbers = initNumbers();
// 再帰を利用したループ処理
mapper
= nums -> (nums.size() <= 1) ? nums.get(0): nums.remove(0) + mapper.map(nums);
Integer sum = mapper.map(numbers);
System.out.println(sum);
}
private List<Integer> initNumbers() {
List<Integer> numbers = new LinkedList<>();
for (int i = 1; i <= 10; i++) {
numbers.add(i);
}
return numbers;
}
public static void main(String... args) {
new NumberAdder();
}
}
import java.util.Arrays;
import java.util.Random;
public class ParallelScoreFinder {
private Random random = new Random();
public ParallelScoreFinder() {
long[] serialTimes = new long[50];
long[] parallelTimes = new long[50];
int maxIndex = 0;
int minIndex = 0;
long max = 0;
long min = 1_000_000_000_000_000L;
// Warm up
for (int i = 0; i < 20; i++) {
findMaxScore();
}
for (int i = 0; i < 50; i++) {
serialTimes[i] = findMaxScore();
if (serialTimes[i] > max) {
maxIndex = i;
} else if (serialTimes[i] < min) {
minIndex = i;
}
}
long sum = 0;
int index = 0;
for (int i = 0; i < 50; i++) {
if (i == minIndex) {
continue;
}
if (i == maxIndex) {
continue;
}
sum += serialTimes[i];
}
System.out.println(index);
System.out.println("Serial Time: " + sum/48/1_000_000);
maxIndex = 0;
minIndex = 0;
max = 0;
min = 1_000_000_000_000_000L;
// Warm up
for (int i = 0; i < 20; i++) {
findMaxScoreParallel();
}
for (int i = 0; i < 50; i++) {
parallelTimes[i] = findMaxScoreParallel();
if (parallelTimes[i] > max) {
maxIndex = i;
} else if (parallelTimes[i] < min) {
minIndex = i;
}
}
sum = 0;
for (int i = 0; i < 50; i++) {
if (i == minIndex) {
continue;
}
if (i == maxIndex) {
continue;
}
sum += parallelTimes[i];
}
System.out.println("Parallel Time: " + sum/48/1_000_000);
}
private long findMaxScore() {
Student[] students = initStudents();
long start = System.nanoTime();
Integer maxScore
= Arrays.asList(students)
.filter(s -> s.getGradYear() == 2011)
.map(Student::getScore)
.reduce(0, Math::max);
long end = System.nanoTime();
return end - start;
}
private long findMaxScoreParallel() {
Student[] students = initStudents();
long start = System.nanoTime();
Integer maxScore
= Arrays.parallel(students)
.filter(s -> s.getGradYear() == 2011)
.map(Student::getScore)
.reduce(0, Math::max);
long end = System.nanoTime();
return end - start;
}
private Student[] initStudents() {
Student[] students = new Student[5_000_001];
for (int i = 0; i <= 5_000_000; i++) {
students[i] = new Student(""+i, random.nextInt(12)+2000, random.nextInt(101));
}
return students;
}
public static void main(String... args) {
new ParallelScoreFinder();
}
}
import java.util.ArrayList;
import java.util.List;
import java.util.Random;
public class ScoreFinder {
private Random random = new Random();
public ScoreFinder() {
List<Student> students = initStudents();
Integer maxScore
= students.filter(s -> s.getGradYear() == 2011)
.map(Student::getScore)
.reduce(0, Math::max);
// いずれで書いてもOK
/*
Integer maxScore
= students.filter(s -> s.getGradYear() == 2011)
.map(s -> s.getScore())
.reduce(0, (s1, s2) -> Math.max(s1, s2));
*/
/*
Integer maxScore
= students.filter(s -> s.getGradYear() == 2011)
.map(s -> s.getScore())
.reduce(0, (s1, s2) -> s1>s2? s1: s2);
*/
System.out.println(maxScore);
}
private List<Student> initStudents() {
List<Student> students = new ArrayList<>();
for (int i = 0; i <= 5_000_000; i++) {
students.add(new Student(""+i, random.nextInt(12)+2000, random.nextInt(101)));
}
return students;
}
public static void main(String... args) {
new ScoreFinder();
}
}
public class Student {
private String name;
private int gradYear;
private int score;
public Student(String name, int gradYear, int score) {
this.name = name;
this.gradYear = gradYear;
this.score = score;
}
public String getName() {
return name;
}
public int getGradYear() {
return gradYear;
}
public int getScore() {
return score;
}
public String toString() {
return "["+name+", year:" + gradYear + ", score:" + score + "]";
}
}
import java.awt.BorderLayout;
import java.awt.FlowLayout;
import java.awt.event.ActionListener;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;
import javax.swing.SwingUtilities;
public class SwingDemoWLambda {
public SwingDemoWLambda() {
JFrame frame = new JFrame("Swing Demo");
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.setSize(400, 150);
JPanel panel = new JPanel();
panel.setLayout(new FlowLayout(FlowLayout.CENTER, 20, 20));
// 実施的 final
JTextField field = new JTextField(20);
panel.add(field);
JButton button = new JButton("Update");
panel.add(button);
frame.add(panel, BorderLayout.NORTH);
// 実施的 final
JLabel label = new JLabel();
label.setHorizontalAlignment(JLabel.CENTER);
frame.add(label, BorderLayout.CENTER);
// field も label も実質的 final であるため、Lambda 式でアクセス可能
ActionListener listener
= event -> { label.setText(field.getText()); };
field.addActionListener(listener);
button.addActionListener(listener);
frame.setVisible(true);
}
public static void main(String... args) {
// 通常の Lambda 式
// SwingUtilities.invokeLater(() -> { new SwingDemoWLambda(); });
// コンストラクタ参照を使用した場合
SwingUtilities.invokeLater(SwingDemoWLambda::new);
}
}
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