Java 流应用编程接口–过滤器
在本文中，我们将学习 Java 流过滤器应用编程接口。我们会报道，
1.流过滤器 API 如何工作。
2.按对象属性筛选。
3.按索引筛选。
4.按自定义对象属性筛选。
流过滤器应用编程接口
过滤器应用编程接口采用谓词。谓词是一个函数接口。它接受任何类型的参数并返回布尔值。如果函数返回 true，则该元素将被考虑用于管道中的下一个应用编程接口。否则，该元素将被过滤掉。
Java 语言(一种计算机语言，尤用于创建网站)
// Java code for Stream filter
// (Predicate predicate) to get a stream
// consisting of the elements of this
// stream that match the given predicate.
import java.io.*;
import java.util.stream.Stream;
class StreamFilterExample {
public static void main(String[] args)
{
// create a stream of strings
Stream<String> myStream
= Stream.of("Like", "and", "Share",
"https://www.geeksforgeeks.org/");
// only string starting with "http://" will be
// considered for next API(forEach)
myStream.filter(x -> x.startsWith("https://"))
.forEach(System.out::println);
}
}
Output
https://www.geeksforgeeks.org/
按对象属性过滤
按对象属性筛选使用 java 运算符。下面的示例解释了如何根据对象的属性进行筛选。
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate
// filter by Object properties
import java.io.*;
import java.util.stream.Stream;
class FilterByObjectProperties {
public static void filterByEvenElements()
{
// create integer array
Integer[] myArray
= new Integer[] { 1, 4, 5, 7, 9, 10 };
// create a stream and filter by
// even numbers predicate
Stream.of(myArray)
.filter(x -> x % 2 == 0)
.forEach(System.out::println);
}
public static void filterByStartsWith()
{
// create String array
String[] myArray
= new String[] { "stream", "is", "a",
"sequence", "of", "elements",
"like", "list" };
// create a stream and filter by
// starting string predicate
Stream<String> myStream = Stream.of(myArray);
myStream.filter(x -> x.startsWith("s"))
.forEach(System.out::println);
}
public static void filterByStartsWithVowelsRegex()
{
// create string array
String[] myArray
= "I am 24 years old and I want to be in Tier I company"
.split(" ");
// create a stream on myArray
Stream<String> myStream = Stream.of(myArray);
// filter by matching vowels regular expression
myStream.filter(x -> x.matches("(a|e|i|o|u)\\w*"))
.forEach(System.out::println);
}
public static void main(String[] args)
{
// filters a stream by even elements
filterByEvenElements();
System.out.println("======");
// filters a stream by starting string
filterByStartsWith();
System.out.println("======");
// filters a stream by starting vowel
filterByStartsWithVowelsRegex();
}
}
Output
4
10
======
stream
sequence
======
am
old
and
in
按对象索引过滤
按索引过滤有两种方式。
1。原子整数
我们需要使用 AtomicInteger ，因为谓词期望最终变量作为参数。只要过滤函数(谓词)返回布尔值，我们就可以使用任何表达式。这里，AtomicInteger 的 getAndIncrement() 方法将当前值增加 1 ，并返回最终的 int 值。
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate
// filter by Object Indices
// using AtomicInteger
import java.io.*;
import java.util.stream.Stream;
import java.util.concurrent.atomic.AtomicInteger;
class FilterByObjectIndex {
public static void filterByIndexUsingAtomic()
{
// create a string array
String[] myArray
= new String[] { "stream", "is", "a",
"sequence", "of", "elements",
"like", "list" };
// create a stream on myArray
Stream<String> myStream = Stream.of(myArray);
// create an AtomicInteger
AtomicInteger i = new AtomicInteger(0);
// increment the i value by 1 everytime
// if it is even, print the current element
myStream.filter(x -> i.getAndIncrement() % 2 == 0)
.forEach(System.out::println);
}
public static void main(String[] args)
{
// filter by Object index
filterByIndexUsingAtomic();
}
}
Output
stream
a
of
like
2。输入流方法
我们可以使用 Intstream 并根据索引映射数组元素。这里我们首先创建一个由一系列数字组成的数据流。检查一个数字是否为偶数，然后用数组元素覆盖/映射该整数。
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate
// filter by Object properties
// using IntSteam Approach
import java.io.*;
import java.util.stream.IntStream;
class FilterByObjectIndexUsingIntStream {
public static void filterByIndexUsingStream()
{
// create an array of Strings
String[] myArray
= new String[] { "stream", "is", "a",
"sequence", "of", "elements",
"like", "list" };
// create instream on range of integers
// filter by even integer and map
// the integer to the Object of myArray
IntStream.rangeClosed(0, myArray.length - 1)
.filter(x -> x % 2 == 0)
.mapToObj(x -> myArray[x])
.forEach(System.out::println);
}
public static void main(String[] args)
{
filterByIndexUsingStream();
}
}
Output
stream
a
of
like
按自定义属性过滤
我们可以使用任何 Java 对象属性进行过滤。这里我们按年龄过滤。
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate
// filter by Custom Properties
import java.io.*;
import java.util.List;
import java.util.Arrays;
import java.util.stream.Stream;
class CustomFiltering {
// Employee class
class Employee {
// attributes of an Employee
String name;
int age;
// constructor
Employee(String name, int age)
{
this.name = name;
this.age = age;
}
// Override toString to print
// provided content when an Object
// is printed
@Override public String toString()
{
return "Employee [name=" + name + "]";
}
}
public static void filterByAge()
{
// create list of Employees
List<Employee> myList = Arrays.asList(
new GFG().new Employee("Ram", 25),
new GFG().new Employee("Kumar", 40),
new GFG().new Employee("Rakesh", 35));
// create a stream on the list
// filter by age of an employee
myList.stream()
.filter(x -> x.age >= 35)
.forEach(System.out::println);
}
public static void main(String[] args)
{
filterByAge();
}
}
Output
Employee [name=Kumar]
Employee [name=Rakesh]
我们还可以创建一个自定义的过滤函数。该函数必须接受一个参数并返回一个布尔值。
Java 语言(一种计算机语言，尤用于创建网站)
// Java program to demonstrate
// Custom filter
import java.io.*;
import java.util.stream.Stream;
class CustomFilterExample {
public static void filterByCustomProperties()
{
// create a string array
String[] myArray
= new String[] { "madam", "please", "refer",
"link", "on", "racecar" };
// filter using a custom method
Stream.of(myArray)
.filter(x -> palindrome(x))
.forEach(System.out::println);
}
// checks if palindrome or not
public static boolean palindrome(String s)
{
if (s.length() <= 1)
return true;
else
return (s.charAt(0) == s.charAt(s.length() - 1))
&& palindrome(
s.substring(1, s.length() - 1));
}
public static void main(String[] args)
{
filterByCustomProperties();
}
}
Output
madam
refer
racecar
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