::方法使用
条件：lambada表达式的主体仅包含一个表达式，且lambada表达式只调用一个已经存在的方法；被引用的方法的参数列表与lambada表达式的输入输出一致
以下是Java 8中方法引用的一些语法：
- 静态方法引用（static method）语法：
classname::methodname例如：Person::getAge - 对象的实例方法引用语法：
instancename::methodname例如：System.out::println - 对象的超类方法引用语法：
super::methodname - 类构造器引用语法：
classname::new例如：ArrayList::new - 数组构造器引用语法：
typename[]::new例如：String[]:new
DataStreamSource<String> kafkaDS = env.addSource(MyKafkaUtil.getKafkaConsumer(sourceTopic, groupId)); kafkaDS.map(line->{return JSON.parseObject(line);}); //Lambda 简写 kafkaDS.map(JSON::parseObject);
@Test void printTest1() { List<String> list = Arrays.asList("a", "b", "c", "d"); System.out.println("for => "); for (String item : list) { AcceptMethod.printValue(item); } System.out.println("forEach => "); list.forEach(item -> AcceptMethod.printValue(item)); System.out.println("forEach => ：："); //list.forEach(new AcceptMethod()::printValue); //非静态方法 list.forEach(AcceptMethod::printValue); System.out.println("forEach list => ：："); List<LoginUser> loginUserList = new ArrayList<>(); LoginUser loginUser = new LoginUser(); loginUser.setOs("iOS"); loginUserList.add(loginUser); loginUser = new LoginUser(); loginUser.setOs("Android"); loginUserList.add(loginUser); loginUserList.forEach(AcceptMethod::printList); } public static class AcceptMethod { public static void printValue(String str) { System.out.println("print value : " + str); } public static void printList(LoginUser map) { System.out.println("print value : " + map.getOs()); } }
Stream 示例
public class Java8Tester { public static void main(String args[]){ System.out.println("使用 Java 7: "); // 计算空字符串 List<String> strings = Arrays.asList("abc", "", "bc", "efg", "abcd","", "jkl"); System.out.println("列表: " +strings); long count = getCountEmptyStringUsingJava7(strings); System.out.println("空字符数量为: " + count); count = getCountLength3UsingJava7(strings); System.out.println("字符串长度为 3 的数量为: " + count); // 删除空字符串 List<String> filtered = deleteEmptyStringsUsingJava7(strings); System.out.println("筛选后的列表: " + filtered); // 删除空字符串，并使用逗号把它们合并起来 String mergedString = getMergedStringUsingJava7(strings,", "); System.out.println("合并字符串: " + mergedString); List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5); // 获取列表元素平方数 List<Integer> squaresList = getSquares(numbers); System.out.println("平方数列表: " + squaresList); List<Integer> integers = Arrays.asList(1,2,13,4,15,6,17,8,19); System.out.println("列表: " +integers); System.out.println("列表中最大的数 : " + getMax(integers)); System.out.println("列表中最小的数 : " + getMin(integers)); System.out.println("所有数之和 : " + getSum(integers)); System.out.println("平均数 : " + getAverage(integers)); System.out.println("随机数: "); // 输出10个随机数 Random random = new Random(); for(int i=0; i < 10; i++){ System.out.println(random.nextInt()); } System.out.println("使用 Java 8: "); System.out.println("列表: " +strings); count = strings.stream().filter(string->string.isEmpty()).count(); System.out.println("空字符串数量为: " + count); count = strings.stream().filter(string -> string.length() == 3).count(); System.out.println("字符串长度为 3 的数量为: " + count); filtered = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.toList()); System.out.println("筛选后的列表: " + filtered); mergedString = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.joining(", ")); System.out.println("合并字符串: " + mergedString); squaresList = numbers.stream().map( i ->i*i).distinct().collect(Collectors.toList()); System.out.println("Squares List: " + squaresList); System.out.println("列表: " +integers); IntSummaryStatistics stats = integers.stream().mapToInt((x) ->x).summaryStatistics(); System.out.println("列表中最大的数 : " + stats.getMax()); System.out.println("列表中最小的数 : " + stats.getMin()); System.out.println("所有数之和 : " + stats.getSum()); System.out.println("平均数 : " + stats.getAverage()); System.out.println("随机数: "); random.ints().limit(10).sorted().forEach(System.out::println); // 并行处理 count = strings.parallelStream().filter(string -> string.isEmpty()).count(); System.out.println("空字符串的数量为: " + count); } private static int getCountEmptyStringUsingJava7(List<String> strings){ int count = 0; for(String string: strings){ if(string.isEmpty()){ count++; } } return count; } private static int getCountLength3UsingJava7(List<String> strings){ int count = 0; for(String string: strings){ if(string.length() == 3){ count++; } } return count; } private static List<String> deleteEmptyStringsUsingJava7(List<String> strings){ List<String> filteredList = new ArrayList<String>(); for(String string: strings){ if(!string.isEmpty()){ filteredList.add(string); } } return filteredList; } private static String getMergedStringUsingJava7(List<String> strings, String separator){ StringBuilder stringBuilder = new StringBuilder(); for(String string: strings){ if(!string.isEmpty()){ stringBuilder.append(string); stringBuilder.append(separator); } } String mergedString = stringBuilder.toString(); return mergedString.substring(0, mergedString.length()-2); } private static List<Integer> getSquares(List<Integer> numbers){ List<Integer> squaresList = new ArrayList<Integer>(); for(Integer number: numbers){ Integer square = new Integer(number.intValue() * number.intValue()); if(!squaresList.contains(square)){ squaresList.add(square); } } return squaresList; } private static int getMax(List<Integer> numbers){ int max = numbers.get(0); for(int i=1;i < numbers.size();i++){ Integer number = numbers.get(i); if(number.intValue() > max){ max = number.intValue(); } } return max; } private static int getMin(List<Integer> numbers){ int min = numbers.get(0); for(int i=1;i < numbers.size();i++){ Integer number = numbers.get(i); if(number.intValue() < min){ min = number.intValue(); } } return min; } private static int getSum(List numbers){ int sum = (int)(numbers.get(0)); for(int i=1;i < numbers.size();i++){ sum += (int)numbers.get(i); } return sum; } private static int getAverage(List<Integer> numbers){ return getSum(numbers) / numbers.size(); } }
实例
/** * java list 中的字符是否包括在另一个 list 中 */ @Test void anyMatchTest() { List<String> permission = Arrays.asList("A", "B", "D"); List<String> arr = Arrays.asList("C", "D", "E", "F"); boolean b = arr.stream().anyMatch(permission::contains); System.out.println("" + b); } /** * 数组转Set\List */ void anyMatchTest() { String[] permsArr = "a,b,c".split(","); Set<String> permsSet = Arrays.stream(permsArr).collect(Collectors.toSet()); }
