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Java 8 Stream reduce method example.
The Stream.reduce() method is a reduction operation. A reduction operation takes a sequence of input elements and
combines them into a single summary result by repeated application of a combining operation. The Stream.reduce() method comes with
three variations.
Stream.reduce() with Accumulator
It performs a reduction on the elements of the given stream, using given accumulation function.
package com.java2novice.streams;
import java.util.stream.Stream;
public class StreamReduceAccEx {
public static void main(String[] args) {
Stream.of(10,20,22,12,14).reduce((x,y)->x+y).ifPresent(System.out::println);
Stream.of(10,20,22,12,14).reduce(Integer::sum).ifPresent(System.out::println);
Stream.of("java", "c", "c#", "python").reduce((x,y)->x+" | "+y).ifPresent(System.out::println);
}
}
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Output: |
78
78
java | c | c# | python
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Stream.reduce() with Identity and Accumulator
It performs a reduction on the elements of the given stream, using given identity value and an accumulation
function. Here the identity is a starting value.
package com.java2novice.streams;
import java.util.stream.Stream;
public class StreamReduceAccEx {
public static void main(String[] args) {
Integer arrSum = Stream.of(10,20,22,12,14).reduce(1000, Integer::sum);
System.out.println(arrSum);
arrSum = Stream.of(10,20,22,12,14).reduce(1000, (x,y)->x+y);
System.out.println(arrSum);
String result = Stream.of("java", "c", "c#", "python").reduce("Languages:", (x,y)->x+" | "+y);
System.out.println(result);
}
}
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Output: |
1078
1078
Languages: | java | c | c# | python
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Stream.reduce() with Identity, Accumulator and Combiner
It performs a reduction on the elements of the given stream, using given identity value, an accumulation
function and combining functions. The identity value must be an identity for the combiner function. Combiner is a
function which aggregates results of the accumulator. Combiner is called only in a parallel mode to reduce results of
accumulators from different threads.
package com.java2novice.streams;
import java.util.stream.Stream;
public class StreamReduceAccEx {
public static void main(String[] args) {
Integer arrSum = Stream.of(10,20,22,12,14).parallel().reduce(1000, (x,y)->x+y, (p,q)->{
System.out.println("combiner called");
return p+q;
});
System.out.println(arrSum);
}
}
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Output: |
combiner called
combiner called
combiner called
combiner called
5078
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Java 8 Streams Examples
- How Java 8 Streams work?
- Java 8 Streams parallelism introduction.
- Explain non-interference behavior of Java 8 Streams.
- Create Java 8 Stream using Stream.of() method example.
- Create Java 8 Stream using List example.
- Create Java 8 Stream using Stream.generate() method.
- Java 8 Stream.filter() example.
- Java 8 Stream.map() example.
- Java 8 Stream flatmap method example.
- Java 8 Stream peek method example.
- Java 8 Stream distinct method example.
- Java 8 Stream sorted method example.
- Java 8 Stream limit method example.
- Java 8 Stream forEach method example.
- Java 8 Stream toArray method example.
- Java 8 Stream reduce method example.
- Java 8 Stream collect method example.
- Java 8 Stream concat method example.
- Java 8 Stream anyMatch(), allMatch() and noneMatch() example.
- Java 8 Stream findFirst(), findAny() example.
- Primitive type Stream example.
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Domain Naming Service(DNS)
It is very difficult to remember a set of numbers (IP address) to connect to the Internet. The Domain Naming Service(DNS) is used to overcome
this problem. It maps one particular IP address to a string of characters. For example, www.java2novice.com implies com is the domain name
reserved for US commercial sites, java2novice is the name of the company and www is the name of the specific computer, which is java2novice's server.
Success consists of going from failure to failure without loss of enthusiasm.
-- Winston Churchill
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