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Java8里面Predicate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和Predicate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 list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

Predicate predicate1 = x -> x > 3;

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

System.out.println(collect);

}

}

输出：

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

2、Predicate 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 list = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);

Predicate predicate1 = x -> x > 3;

Predicate predicate2 = x -> x < 9;

List 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 list = Arrays.asList("java","c++","c","c#","php","kotlin","javascript");

Predicate predicate1 = x -> x.length() > 3;

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

List 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 list = Arrays.asList("java","c++","c","c#","php","kotlin","javascript");

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

List 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 list = Arrays.asList("java", "c++", "c", "c#", "php", "kotlin", "javascript");

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

List 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 list = Arrays.asList("java", "c++", "c", "c#", "php", "kotlin", "javascript");

Predicate 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 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 students = Arrays.asList(student1, student2, student3);

BiPredicate biPredicate = (age, name) -> (age >= 30 && name.equals("mars"));

List ret = filter(students, biPredicate);

System.out.println(ret);

}

public static List filter(List stu, BiPredicate 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}]