Java8 lambda表达式10个示例

package cjj.online.cn;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.util.Arrays;
import java.util.IntSummaryStatistics;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

import javax.swing.JButton;

/**
* @author:蔡佳君
* @date:2017年12月7日 下午5:24:53
* @version:
* @description:
*/
public class Threadtest1Lambda {

public static void main(String[] args) {
// 1. 用lambda表达式实现Runnable
// java 8之前
new Thread(new Runnable() {
@Override
public void run() {
System.out.println("Before Java8,too much too little to do");
}
}).start();
// java 8 Lambda方式
new Thread(() -> System.out
.println("In Java8, Lambda expression rocks!!!")).start();
System.out.println("1. ------------------------------");
// 2. 使用Java 8 lambda表达式进行事件处理
// java 8之前
JButton show = new JButton("show");
show.addActionListener(new ActionListener() {

@Override
public void actionPerformed(ActionEvent e) {
System.out.println(
"Event handling without lambda expression is boring");
}
});
// java 8之后
show.addActionListener((e) -> {
System.out.println(
"Light, Camera, Action !! Lambda expressions Rocks");
});
System.out.println("2. ------------------------------");
// 3. 使用lambda表达式对列表进行迭代
// java 8前
List<String> features = Arrays.asList("Lambdas", "Default Method",
"Stream API", "Date and Time API");
for (String feature : features) {
System.out.println(feature);
}
System.out.println("3. ------------------------------");
// java 8之后
List<String> featrues = Arrays.asList("Lambdas", "Default Method",
"Stream API", "Date and Time API");
features.forEach(n -> System.out.println(n));
// java8后得 ：：双冒号表示、范围解析操作符现在在Java 8中用来表示方法引用,
features.forEach(System.out::println);
System.out.println("3. ------------------------------");

// 4. 使用lambda表达式和函数式接口Predicate 把数组转换成List集合Arrays.asList();
System.out.println("4 ------------------------------");
List<String> languages = Arrays.asList("Java", "Scala", "C++",
"Haskell", "Lisp");

System.out.println("Languages which starts with J :");
// (str) -> ((String) str).startsWith("J") 遍历集合List,并取出首字母包含J的集合项
filter(languages, (str) -> ((String) str).startsWith("J"));
System.out.println("Languages which ends with a ");
filter(languages, (str) -> ((String) str).endsWith("a"));
System.out.println("Print all languages :");
filter(languages, (str) -> true);
System.out.println("Print no language : ");
filter(languages, (str) -> false);
System.out.println("Print language whose length greater than 4:");
filter(languages, (str) -> ((String) str).length() > 4);
// 5、如何在lambda表达式中加入Predicate
// 甚至可以用and()、or()和xor()逻辑函数来合并Predicate，
// 例如要找到所有以J开始，长度为四个字母的名字，你可以合并两个Predicate并传入
System.out.println("5 ------------------------------");
List<String> names = Arrays.asList("Java", "Scala", "C++", "Haskell",
"Lisp");
Predicate<String> startsWithJ = (n) -> n.startsWith("J");
Predicate<String> fourLetterLong = (n) -> n.length() == 4;
names.stream().filter(startsWithJ.and(fourLetterLong))
.forEach((n) -> System.out
.print("nName, which starts with 'J' and four letter long is : "
+ n));
System.out.println();
// 6、Java 8中使用lambda表达式的Map和Reduce示例
System.out.println("6.1 ------------------------------");
// 不使用lambda表达式为每个订单加上12%的税
List<Integer> costBeforeTax = Arrays.asList(100, 200, 300, 400, 500);
for (Integer cost : costBeforeTax) {
double price = cost + .12 * cost;
System.out.println(price);
}
System.out.println("6.1 ------------------------------");
// 使用lambda表达式
List<Integer> costBeforeTax1 = Arrays.asList(100, 200, 300, 400, 500);
costBeforeTax1.stream().map((cost) -> cost + .12 * cost)
.forEach(System.out::println);
// 6.2、Java 8中使用lambda表达式的Map和Reduce示例
System.out.println("6.2 ------------------------------");
// 为每个订单加上12%的税
// 老方法：
List<Integer> costBeforeTax2 = Arrays.asList(100, 200, 300, 400, 500);
double total = 0;
for (Integer cost : costBeforeTax2) {
double price = cost + .12 * cost;
total = total + price;
}
System.out.println("Total : " + total);

// 新方法：reduce 接收多个值并返回一个值
// Java中Arrays的asList()方法 可以将 数组转为List 但是，这个数组类型必须是 引用类型的
System.out.println("6.2 ------------------------------");
List<Integer> costBeforeTax3 = Arrays.asList(100, 200, 300, 400, 500);
double bill = costBeforeTax3.stream().map((cost) -> cost + .12 * cost)
.reduce((sum, cost) -> sum + cost).get();
System.out.println("Total : " + bill);

// 7. 创建一个字符串列表，每个字符串长度大于2
// collect()操作会把其接收的元素聚集（aggregate）到一起（这里是List），
// collect()方法的参数则被用来指定如何进行聚集操作。在这里我们使用toList()以把元素输出到List中。
// filter()有一种遍历的意思
System.out.println("7 ------------------------------");
List<String> strList = Arrays.asList("Lambdas", "Default Method",
"Stream API", "Date and Time API");
List<String> filtered = strList.stream().filter(x -> x.length() > 10)
.collect(Collectors.toList());
System.out.printf("Original List : %s, filtered list : %s %n", strList,
filtered);
// 8、对列表的每个元素应用函数
// 将字符串换成大写并用逗号链接起来
System.out.println("8 ------------------------------");
List<String> G7 = Arrays.asList("USA", "Japan", "France", "Germany",
"Italy", "U.K.", "Canada");
String G7Countries = G7.stream().map(x -> x.toUpperCase())
.collect(Collectors.joining(", "));
System.out.println(G7Countries);
// 9、复制不同的值，创建一个子列表
// 利用流的 distinct() 方法来对集合进行去重
// 用所有不同的数字创建一个正方形列表
System.out.println("9 ------------------------------");
List<Integer> numbers = Arrays.asList(9, 10, 3, 4, 7, 3, 4);
List<Integer> distinct = numbers.stream().map(i -> i * i).distinct()
.collect(Collectors.toList());
System.out.printf(
"Original List : %s,  Square Without duplicates : %s %n",
numbers, distinct);
// 10、计算集合元素的最大值、最小值、总和以及平均值
// 获取数字的个数、最小值、最大值、总和以及平均值
System.out.println("10------------------------------");
List<Integer> primes = Arrays.asList(2, 3, 5, 7, 11, 13, 17, 19, 23,
29);
IntSummaryStatistics stats = primes.stream().mapToInt((x) -> x)
.summaryStatistics();
System.out.println("Highest prime number in List : " + stats.getMax());
System.out.println("Lowest prime number in List : " + stats.getMin());
System.out.println("Sum of all prime numbers : " + stats.getSum());
System.out.println(
"Average of all prime numbers : " + stats.getAverage());

}

public static void filter(List names, Predicate condition) {
names.stream().filter((name) -> (condition.test(name)))
.forEach((name) -> {
System.out.println(name + " ");
});
}
}