jdk8 forEach

分手后的思念是犯贱 2022-06-05 00:45 202阅读 0赞

### 源码 ###

forEach是jdk8的新特性，其源码如下：

/** * Performs the given action for each element of the {@code Iterable} * until all elements have been processed or the action throws an * exception. Unless otherwise specified by the implementing class, * actions are performed in the order of iteration (if an iteration order * is specified). Exceptions thrown by the action are relayed to the * caller. * * @implSpec * <p>The default implementation behaves as if: * <pre>{@code * for (T t : this) * action.accept(t); * }</pre> * * @param action The action to be performed for each element * @throws NullPointerException if the specified action is null * @since 1.8 */
    default void forEach(Consumer<? super T> action) {
        Objects.requireNonNull(action);
        for (T t : this) {
            action.accept(t);
        }
    }

### 应用 ###

观察源码发现,forEach需要传入Consumer

@Test
    public void testForEachOfJdk8(){
        List<Map<String,String>> listMap = new ArrayList<>() ;
    
        getListMap().forEach(new MyConsumer(listMap));
        System.out.println(listMap.toString()) ;
    }
    
    // 组装list，用以forEach
    private List<Map<String,String>> getListMap() {
        List<Map<String,String>> listMap = new ArrayList<>() ;
        for(int i=1;i<=3;i++){
            Map<String,String> map = new HashMap<>() ;
            map.put(String.valueOf(i),String.valueOf(i)) ;
            listMap.add(map) ;
        }
        return listMap ;
    }
    
    class MyConsumer implements Consumer<Map<String,String>>{
        List<Map<String,String>> listMap = new ArrayList<>() ;
        public MyConsumer(List<Map<String,String>> listMap) {
            this.listMap = listMap ;
        }
        @Override
        public void accept(Map<String, String> stringStringMap) {
            listMap.add(stringStringMap) ;
        }
    }

### 拓展 ###

引入limbda表达式，可简写

@Test
    public void testForEachOfJdk8Of2(){
        List<Map<String,String>> listMap = new ArrayList<>() ;
        getListMap().forEach((Map<String,String> maps) -> {
            listMap.add(maps) ;
        });
        System.out.println(listMap.toString()) ;
    }
    
    // 组装list，用以forEach
    private List<Map<String,String>> getListMap() {
        List<Map<String,String>> listMap = new ArrayList<>() ;
        for(int i=1;i<=3;i++){
            Map<String,String> map = new HashMap<>() ;
            map.put(String.valueOf(i),String.valueOf(i)) ;
            listMap.add(map) ;
        }
        return listMap ;
    }

进一步简写

@Test
    public void testForEachOfJdk8Of2(){
        List<Map<String,String>> listMap = new ArrayList<>() ;
        getListMap().forEach(maps -> listMap.add(maps));
        System.out.println(listMap.toString()) ;
    }
    
    // 组装list，用以forEach
    private List<Map<String,String>> getListMap() {
        List<Map<String,String>> listMap = new ArrayList<>() ;
        for(int i=1;i<=3;i++){
            Map<String,String> map = new HashMap<>() ;
            map.put(String.valueOf(i),String.valueOf(i)) ;
            listMap.add(map) ;
        }
        return listMap ;
    }

### 尾声 ###

欢迎大家纠正