Java 8新特性之Predicate（三）

简介

核心方法 boolean test(T t) : 数据验证，返回布尔类型的值。

源码分析

@FunctionalInterface
public interface Predicate<T> {

	//传入参数t,返回一个布尔值
    boolean test(T t);

	//与操作
    default Predicate<T> and(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) && other.test(t);
    }

	//取反操作
    default Predicate<T> negate() {
        return (t) -> !test(t);
    }

	//或操作
    default Predicate<T> or(Predicate<? super T> other) {
        Objects.requireNonNull(other);
        return (t) -> test(t) || other.test(t);
    }

	//静态方法，比较两个对象是否一致
    static <T> Predicate<T> isEqual(Object targetRef) {
        return (null == targetRef)
                ? Objects::isNull
                : object -> targetRef.equals(object);
    }
}

使用示例

@ApiModel(value = "Predicate")
public class PredicateDemo1 {

    @Test
    @ApiModelProperty(value = "predicate.test方法")
    public void predicateTest () {
        boolean flag = predicateTrueOrFalse("wangjiesheng", s->s.equals("wangjiesheng"));
        Console.log("predicateTest-->{}", flag);
        //输出：predicateTest-->true
    }

    public <T> boolean predicateTrueOrFalse (T t, Predicate<T> predicate) {
        return predicate.test(t);
    }

    @Test
    @ApiModelProperty(value = "predicate.and.test 方法")
    public void predicateAndTest () {
        boolean flag = predicateAnd("wangjiesheng", s->s.equals("wangjiesheng"), s -> s.length() == 12);
        Console.log("predicateAndTest-->{}", flag);
        //输出：predicateAndTest-->true

        flag = predicateAnd("wangjiesheng", s->s.equals("wangjiesheng"), s -> s.length() == 11);
        Console.log("predicateAndTest-->{}", flag);
        //输出：predicateAndTest-->false
    }

    //先执行predicate，再执行predicate2 and连接 两者必须都是true 结果才是true
    public <T> boolean predicateAnd (T t, Predicate<T> predicate, Predicate<T> predicate2) {
        return predicate.and(predicate2).test(t);
    }

    @Test
    @ApiModelProperty(value = "predicate.or.test 方法")
    public void predicateOrTest () {
        boolean flag = predicateOr("wangjiesheng", s->s.equals("wangjiesheng"), s -> s.length() == 12);
        Console.log("predicateOrTest-->{}", flag);
        //输出：predicateOrTest-->true

        flag = predicateOr("wangjiesheng", s->s.equals("wangjiesheng"), s -> s.length() == 11);
        Console.log("predicateOrTest-->{}", flag);
        //输出：predicateOrTest-->true
    }

    //先执行predicate，再执行predicate2 or连接 其中有一个是true 结果就是true
    public <T> boolean predicateOr (T t, Predicate<T> predicate, Predicate<T> predicate2) {
        return predicate.or(predicate2).test(t);
    }

    @Test
    @ApiModelProperty(value = "predicate.negate.test 方法")
    public void predicateNegateTest () {
        boolean flag = predicateNegate("wangjiesheng", s->s.equals("wangjiesheng"));
        Console.log("predicateNegateTest-->{}", flag);
        //输出：predicateNegateTest-->false
    }

    //执行predicate 取反操作
    public <T> boolean predicateNegate (T t, Predicate<T> predicate) {
        return predicate.negate().test(t);
    }
}

总结

使用Predicate可以让你的判断逻辑代码更加的简洁和解耦，增加了可读性、可测试性，同时符合DRY原则。

DRY原则：(don’t repeat yourself): writing code more than once is not a good fit for a lazy developer ;)It also makes your software more difficult to maintain because it becomes harder to make your business logic consistent。一句话：别写重复代码