Function Bifunction实践

函数编程中的两个东西 Function

@FunctionalInterface
public interface Function<T, R> {

    /**
     * Applies this function to the given argument.
     *
     * @param t the function argument
     * @return the function result
     */
    R apply(T t);

复制一点源码可以看到,入参为两个 调用apply 返回给定结果R

BiFunction

@FunctionalInterface
public interface BiFunction<T, U, R> {

    /**
     * Applies this function to the given arguments.
     *
     * @param t the first function argument
     * @param u the second function argument
     * @return the function result
     */
    R apply(T t, U u);

复制一点源码,可以看到,入参为三个参数,调用apply 返回指定结果R

具体要怎么使用呢?举两个栗子:
1 Function
比如我要实现: list中的元素的id的提取,下面为测试代码

@Test
    void 测试函数() {
        List<Tree> trees = initList();//初始化一些集合 随意

        List<String> ids = Lists.newArrayList();

        trees.forEach(tree -> {
            ApplyFunction applyFunction = new ApplyFunction(Tree::getId);//真正执行的方法
            ids.add(applyFunction.getGetId().apply(tree));// 执行入口
        });

        ids.forEach(s -> System.out.println(s));

    }

粘贴出ApplyFunction 代码

@Data
public class ApplyFunction {

    private Function<Tree,String> getId;

    public ApplyFunction(Function<Tree,String> getId) {
        this.getId = getId;
    }

}

这样就ok了,通过Function实现了一些自定义过滤,当然也可以很复杂

2 Bifunction
比如我要实现,两个集合中的对应位置的元素是否相等(相等的条件我自己定义)
下面为测试代码

@Autowired
    EqualsFunction equalsFunction;

@Test
    void 是否一致() {
        List<Tree> trees = initList();
        List<Tree> trees1 = initList1();

        int size = trees.size();

        if (trees.size()>trees1.size()) {
            size = trees1.size();
        }

        for (int i = 0; i < size; i++) {
            Tree tree = trees.get(i);
            Tree tree1 = trees1.get(i);

            Boolean equal = (Boolean) equalsFunction.isEqual(tree, tree1);

            System.out.print(JSONUtil.toJsonStr(tree));
            System.out.print(JSONUtil.toJsonStr(tree1));
            System.out.println(equal);
        }
    }

粘贴下打印结果

{"pid":"root","id":"0"}{"pid":"root","id":"0"}true
{"pid":"0","id":"1"}{"pid":"0","id":"1"}true
{"pid":"0","id":"2"}{"pid":"10","id":"2"}false
{"pid":"2","id":"6"}{"pid":"12","id":"6"}false
{"pid":"6","id":"7"}{"pid":"16","id":"7"}false
{"pid":"1","id":"3"}{"pid":"11","id":"3"}false
{"pid":"1","id":"4"}{"pid":"11","id":"4"}false
{"pid":"4","id":"5"}{"pid":"4","id":"5"}true
{"pid":"6","id":"7"}{"pid":"6","id":"7"}true
{"pid":"4","id":"5"}{"pid":"4","id":"5"}true

粘贴另外两个类EqualsConfig和EqualsFunction

public class EqualsFunction<P extends Tree,S extends Tree>{

    private BiFunction<Tree, Tree, Boolean> equal;


    public EqualsFunction(BiFunction<Tree, Tree, Boolean> equal) {
        this.equal = equal;
    }



    public Object isEqual(Tree tree, Tree tree1){
        Boolean apply = equal.apply(tree, tree1);
        return apply;
    }
}

@Component
public class EqualsConfig{

    @Bean
    public EqualsFunction registerEqualsFunction(){
        return new EqualsFunction<>((tree1,tree2)-> ObjectUtils.equals(tree1.getId(),tree2.getId()) && ObjectUtils.equals(tree1.getPid(),tree2.getPid()));
    }
}

至此,完成两个类的比较

具体代码,在我的gitee 中 test项目中

https://gitee.com/flgitee/test