Java 8 CompletableFuture Exception Handling | handle() with NPException ArithmeticException

June 07, 2026

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CompletableFuture Exception Handling | handle() with NPException ArithmeticException

package org.practice.basicprgms;

import java.util.concurrent.CompletableFuture;
import java.util.concurrent.ExecutionException;

public class ExceptionHandlingInCompletableFuture {

	public static void main(String[] args) throws InterruptedException, ExecutionException {
		// 1. Handle ArithmeticException Using exceptionally()
		CompletableFuture<Integer> future1 = 
				CompletableFuture.supplyAsync(() -> {
					int totalSalary = 50000;
					int empCount = 10;
					return totalSalary / empCount;					
				}).exceptionally(ex -> {
					System.out.println("Exception : "+ ex.getMessage());
					return -1;
				});
		System.out.println("Average Salary : "+ future1.get());
				
		// 2. Handle NullPointerException Using exceptionally()
		CompletableFuture<Integer> future2 = 
				CompletableFuture.supplyAsync(() -> {
					String name = "Yogesh";
					return name.length();
				}).exceptionally(ex -> {
					System.out.println("Exception : "+ ex.getMessage());
					return -1;
				});
		System.out.println("Length : "+ future2.get());
		
		
		// 3. Handle Multiple Exception Using handle() method
		CompletableFuture<Integer> future3 =
				CompletableFuture.supplyAsync(() -> {
					String name = "Ronny";
					if(name == null) {
						throw new NullPointerException();
					}
					int salary = 50000;
					int empCount = 10;
					return salary / empCount;
				}).handle((result, ex) -> {
					if(ex != null) {
						Throwable t = ex.getCause();
						
						if(t instanceof NullPointerException)
							return -1;
						else if(t instanceof ArithmeticException)
							return -2;
					}
					return result;
				});
		System.out.println("Average Salary :"+ future3.get());

		// 4. Logged Exception(ArithmeticException) Using whenComplete()
		CompletableFuture<Integer> future4 =
				CompletableFuture.supplyAsync(() -> 100/10)
								.whenComplete((result, ex) -> {
									if(ex != null)
										System.out.println("Exception : "+ ex.getMessage());
								});
		System.out.println("Result future 4 :"+ future4.get());

		// 5. Manually Failed the Future Using completeExceptionally()
		CompletableFuture<Integer> future5 = new CompletableFuture<Integer>();
		future5.completeExceptionally(new RuntimeException("Database Down"));
		
		System.out.println("Exception : "+ future5.get());		
	}
}

Output:
Exception : java.lang.ArithmeticException: / by zero
Average Salary : -1
Exception : java.lang.NullPointerException: Cannot invoke "String.length()" because "name" is null
Length : -1
Average Salary :-1
Exception : java.lang.ArithmeticException: / by zero
Exception in thread "main" java.util.concurrent.ExecutionException: java.lang.ArithmeticException: / by zero
	at java.base/java.util.concurrent.CompletableFuture.reportGet(CompletableFuture.java:396)
	at java.base/java.util.concurrent.CompletableFuture.get(CompletableFuture.java:2073)
	at org.practice.basicprgms.ExceptionHandlingInCompletableFuture.main(ExceptionHandlingInCompletableFuture.java:63)
Caused by: java.lang.ArithmeticException: / by zero
	at org.practice.basicprgms.ExceptionHandlingInCompletableFuture.lambda$6(ExceptionHandlingInCompletableFuture.java:58)
	at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.run(CompletableFuture.java:1768)
	at java.base/java.util.concurrent.CompletableFuture$AsyncSupply.exec(CompletableFuture.java:1760)
	at java.base/java.util.concurrent.ForkJoinTask.doExec(ForkJoinTask.java:373)
	at java.base/java.util.concurrent.ForkJoinPool$WorkQueue.topLevelExec(ForkJoinPool.java:1182)
	at java.base/java.util.concurrent.ForkJoinPool.scan(ForkJoinPool.java:1655)
	at java.base/java.util.concurrent.ForkJoinPool.runWorker(ForkJoinPool.java:1622)
	at java.base/java.util.concurrent.ForkJoinWorkerThread.run(ForkJoinWorkerThread.java:165)