常用Lambda表达式详解

喜欢ヅ旅行 2024-03-23 14:15 72阅读 0赞

##### Lambda表达式遍历List集合 #####

List<String> list = Arrays.asList("A","C","B","D");
    System.out.println("--------------------------");
    list.forEach(a -> System.out.println(a));
    System.out.println("--------------------------");
    list.forEach(System.out::println);

运行结果

--------------------------
    A
    C
    B
    D
    --------------------------
    A
    C
    B
    D

##### Lambda表达式排序List集合 #####

//使用比较器排序
    List<String> list = Arrays.asList("A","C","B","D");
    Collections.sort(list, new Comparator<String>() {
        
    	@Override
    	public int compare(String o1, String o2) {
        
    		return o1.compareTo(o2);
    	}
    });
    System.out.println(list);
    //使用Lambda表达式
    List<String> list1 = Arrays.asList("A","C","B","D");
    Collections.sort(list1, (o1,o2)-> o1.compareTo(o2));
    System.out.println(list1);

运行结果

[A, B, C, D]
    [A, B, C, D]

##### Lambda表达式过滤List集合 #####

//不使用Lambda表达式
    List<String> list = Arrays.asList("Aa","C","aB","D");
    List<String> filterList = new ArrayList<String>();
    for (String str: list) {
        
    	if (str.contains("a")) {
        
    		filterList.add(str);
    	}
    }
    System.out.println(filterList);
    //使用Lambda表达式
    List<String> list1 = Arrays.asList("Aa","C","aB","D");
    List<String> filterList1 = list1.stream().filter(str-> str.contains("a")).collect(Collectors.toList());
    System.out.println(filterList1);

运行结果

[Aa, aB]
    [Aa, aB]

##### Lambda表达式映射集合 #####

//不使用Lambda表达式
    List<String> list = Arrays.asList("Aa","C","aB","D");
    List<Integer> filterList = new ArrayList<Integer>();
    for (String str: list) {
        
    	filterList.add(str.length());
    }
    System.out.println(filterList);
    //使用Lambda表达式
    List<String> list1 = Arrays.asList("Aa","C","aB","D");
    List<Integer> filterList1 = list1.stream().map(str-> str.length()).collect(Collectors.toList());
    System.out.println(filterList1);

运行结果

[2, 1, 2, 1]
    [2, 1, 2, 1]

##### Lambda表达式进行累加 #####

//使用Lambda表达式累加
    List<Integer> list = Arrays.asList(1,2,3,4);
    int sum = list.stream().reduce(0, (a,b) -> a+b);
    System.out.println(sum);

运行结果

##### Lambda表达式进行分组 #####

//不使用Lambda表达式
    List<String> list = Arrays.asList("Aa","C","aB","D");
    Map<Integer, List<String>> groupMap = new HashMap<Integer, List<String>>();
    for (String str: list) {
        
    	if (!groupMap.containsKey(str.length())) {
        
    		groupMap.put((str.length()), new ArrayList<>());
    	}
    	groupMap.get(str.length()).add(str);
    }
    System.out.println(groupMap);
    
    //使用Lambda表达式
    List<String> list1 = Arrays.asList("Aa","C","aB","D");
    Map<Integer, List<String>> groupMap1 = list1.stream().collect(Collectors.groupingBy(str -> str.length()));
    System.out.println(groupMap1);

运行结果

{
        1=[C, D], 2=[Aa, aB]}
    {
        1=[C, D], 2=[Aa, aB]}