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Java LongSupplier Example

By Arvind Rai, May 05, 2020
This page will walk through LongSupplier example. The LongSupplier is the functional interface introduced in Java 8 under the java.util.function package. The LongSupplier is the long-producing primitive specialization of Supplier functional interface. The functional method of LongSupplier is getAsLong() which returns result of long datatype. Find the LongSupplier structure from Java doc.
@FunctionalInterface
public interface LongSupplier {
    long getAsLong();
} 
The LongSupplier can be instantiated using lambda expression and method reference. Here we will provide using LongSupplier in our applications in detail.

Using Lambda Expression

Find the code to instantiate LongSupplier using lambda expression.
LongSupplierWithLE.java
package com.concretepage;
import java.time.LocalDate;
import java.util.function.LongSupplier;
public class LongSupplierWithLE {
  public static void main(String[] args) {
      LongSupplier epochLs = () -> LocalDate.now().toEpochDay();
      System.out.println(epochLs.getAsLong());

      LongSupplier ls = () ->  Long.parseLong("145");
      System.out.println(ls.getAsLong());      
      
      LongSupplier multiplyLs = () -> {
    	long num1 = 30L;
    	long num2 = 50L;
    	return num1 * num2;
      };
      System.out.println(multiplyLs.getAsLong());  
  }
} 
Output
18387
145
1500 

Using Method Reference

Find the code to instantiate LongSupplier using method reference.
LongSupplierWithMR.java
package com.concretepage;
import java.util.Date;
import java.util.function.LongSupplier;
public class LongSupplierWithMR {
  public static void main(String[] args) {
	LongSupplier timeLs = new Date()::getTime;
	System.out.println(timeLs.getAsLong());
	
	LongSupplier dataLs = AppUtil::noOfData;
	System.out.println(dataLs.getAsLong());
  }
}

class AppUtil {
  public static long noOfData() {
	return 1234L;
  }
} 
Output
1588686047879
1234 

Passing as Method Parameter

Here we will pass LongSupplier as method parameter.
WithMethodParameter.java
package com.concretepage;
import java.util.Random;
import java.util.function.LongSupplier;
import java.util.stream.LongStream;
public class WithMethodParameter {
  public static void main(String[] args) {
	String id = createTempId(() -> new Random().nextLong());
	System.out.println(id);

	System.out.println("--- With LongStream.generate() ---");
	LongStream longStream = LongStream.generate(() -> new Random().nextLong()).limit(5);
	longStream.forEach(v -> System.out.println(v));
  }

  static String createTempId(LongSupplier ls) {
	return "temp-id-" + ls.getAsLong();
  }
} 
Output
temp-id-4388374608979425584
--- With LongStream.generate() ---
-4744270447427209101
7914465496616666323
1365939277194664766
6155062943727281293
-1048509395104587980 

Reference

Java doc: LongSupplier
POSTED BY
ARVIND RAI
ARVIND RAI








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