Java 8 Predicate&BiPredicate接口使用

Java8里面Predicate<T>是一个函数式接口，它接受一个参数返回一个boolean类型，通常在集合对象的筛选器中使用，BiPredicate<T, U>和Predicate<T>功能类似，只是多了一个参数。

1、Predicate Hello World

package com.cattles.function;

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/5 下午1:33
 */
public class Java8Predicate1 {

    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

        Predicate<Integer> predicate1 = x -> x > 3;

        List<Integer> collect = list.stream().filter(predicate1).collect(Collectors.toList());

        System.out.println(collect);

    }
}

输出：

[4, 5, 6, 7, 8, 9, 10]

2、Predicate<T> and 方法使用

下面这个例子最终要取得的值是大于3且小于9的数字，我们看一下代码和结果

package com.cattles.function;

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/5 下午3:32
 */
public class Java8Predicate2 {

    public static void main(String[] args) {
        List<Integer> list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
        Predicate<Integer> predicate1 = x -> x > 3;
        Predicate<Integer> predicate2 = x -> x < 9;
        List<Integer> collect = list.stream().filter(predicate1.and(predicate2)).collect(Collectors.toList());
        System.out.println(collect);
    }
}

输出：

[4, 5, 6, 7, 8]

上面是直接使用了Preciate的and方法，我们也可以直接传入 x -> x > 3 & x < 8 得到一样的结果哦

3、Predicate or 方法使用

package com.cattles.function;

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/5 下午3:38
 */
public class Java8Predicate3 {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("java","c++","c","c#","php","kotlin","javascript");

        Predicate<String> predicate1 = x -> x.length() > 3;
        Predicate<String> predicate2 = x -> x.endsWith("+");

        List<String> collect = list.stream().filter(predicate1.or(predicate2)).collect(Collectors.toList());
        System.out.println(collect);
    }
}

输出：

[java, c++, kotlin, javascript]

4、Predicate negate 方法使用

找出集合中不以“+”结尾的所有集合

package com.cattles.function;

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/5 下午3:38
 */
public class Java8Predicate4 {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("java","c++","c","c#","php","kotlin","javascript");

        Predicate<String> predicate2 = x -> x.endsWith("+");

        List<String> collect = list.stream().filter(predicate2.negate()).collect(Collectors.toList());
        System.out.println(collect);
    }
}

输出：

[java, c, c#, php, kotlin, javascript]

5、Predicate test 方法使用

package com.cattles.function;

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/5 下午3:38
 */
public class Java8Predicate5 {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("java", "c++", "c", "c#", "php", "kotlin", "javascript");

        Predicate<String> predicate2 = x -> x.endsWith("+");

        List<String> collect = list.stream().filter(predicate2::test).collect(Collectors.toList());
        System.out.println(collect);
    }
}

[c++]

6、 Predicate 链式调用

package com.cattles.function;

import java.util.Arrays;
import java.util.List;
import java.util.function.Predicate;
import java.util.stream.Collectors;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/5 下午3:38
 */
public class Java8Predicate6 {
    public static void main(String[] args) {
        List<String> list = Arrays.asList("java", "c++", "c", "c#", "php", "kotlin", "javascript");

        Predicate<String> predicate2 = x -> x.startsWith("c");
        //以c开头或者以t结尾
        boolean ret = predicate2.or(x -> x.endsWith("t")).test("javascript");
        System.out.println(ret);

        //!（以c开头且长度等于4）
        boolean ret2 = predicate2.and(x -> x.length() == 4).negate().test("java");
        System.out.println(ret2);
    }
}

输出：

true
true

7、BiPredicate Hello World

package com.cattles.function;

import java.util.function.BiPredicate;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/5 下午3:38
 */
public class Java8BiPredicate1 {
    public static void main(String[] args) {
        BiPredicate<String, Integer> filter = (x, y) -> {
            return x.length() == y;
        };

        boolean ret = filter.test("cattle", 6);
        boolean ret2 = filter.test("java", 8);
        System.out.println(ret);
        System.out.println(ret2);
    }
}

true
false

8、BiPredicate 当作参数使用

找出姓名为mars，年纪大于等于30岁的同学

package com.cattles.function;

import java.util.Arrays;
import java.util.List;
import java.util.function.BiPredicate;
import java.util.stream.Collectors;

/**
 * @author cattle -  稻草鸟人
 * @date 2020/3/5 下午3:38
 */
public class Java8BiPredicate2 {
    public static void main(String[] args) {
        Java8BiPredicate2 obj = new Java8BiPredicate2();
        Student student1 = new Student("cattle", 18);
        Student student2 = new Student("tony", 22);
        Student student3 = new Student("mars", 30);
        List<Student> students = Arrays.asList(student1, student2, student3);

        BiPredicate<Integer, String> biPredicate = (age, name) -> (age >= 30 && name.equals("mars"));
        List<Student> ret = filter(students, biPredicate);
        System.out.println(ret);
    }

    public static <T extends Student> List<T> filter(List<T> stu, BiPredicate<Integer, String> biPredicate) {
        return stu.stream().filter(x -> biPredicate.test(x.getAge(), x.getName())).collect(Collectors.toList());
    }

    static class Student {
        private String name;
        private Integer age;

        public Student(String name, Integer age) {
            this.name = name;
            this.age = age;
        }

        public String getName() {
            return name;
        }

        public void setName(String name) {
            this.name = name;
        }

        public Integer getAge() {
            return age;
        }

        public void setAge(Integer age) {
            this.age = age;
        }

        @Override
        public String toString() {
            return "Student{" +
                    "name='" + name + '\'' +
                    ", age=" + age +
                    '}';
        }
    }
}

输出：

[Student{name='mars', age=30}]

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