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java 8 lambda expresssions exception handling

Posted on 2016-11-14
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Last Modified: 2016-11-29
Hi,
using java 8 lambda expresssions how to do exception handling. please advise
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Question by:gudii9
3 Comments
 
LVL 12

Accepted Solution

by:
Radek Baranowski earned 1000 total points
ID: 41886782
Simple as it is, you can put the code using lambdas within try/catch block and work with expected exceptions like with any other ones. Here's simple example:

import java.util.ArrayList;

public class Lambda {
        
   ArrayList<Node> al;

   // inner class
	private class Node{ 
		double[] a;
		
	}
	
	public Lambda(){
		al = new ArrayList<Node>();
		al.add(new Node());
		al.add(new Node());
		al.add(new Node());
		al.add(new Node());
	}
	
	
	public static void main(String[] args) {
		
		Lambda l = new Lambda();
		try{				
			l.al.forEach( n ->
				System.out.println(n.a[2]*n.a[3])
				);
		} catch (java.lang.NullPointerException e) {
			System.out.println(e);
		}
		
		
	}

}

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LVL 16

Assisted Solution

by:gurpsbassi
gurpsbassi earned 1000 total points
ID: 41886786
I am assuming you are referring to Streams in Java 8?
They do not play well with exceptions. However with Optional types you have the ability to throw exceptions e.g. Optional.orElseThrow(...)


However guddi9 this is a VERY advanced topic for you. I would not recommend you learn this just yet until you are fluent in java up to version 7.
This means being able to decipher if-else control logic without the need for venn diagrams.
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LVL 7

Author Comment

by:gudii9
ID: 41896405
package syout;
import java.util.ArrayList;

public class Lambda {
        
   ArrayList<Node> al;

   // inner class
	private class Node{ 
		double[] a;
		
	}
	
	public Lambda(){
		al = new ArrayList<Node>();
		al.add(new Node());
		al.add(new Node());
		al.add(new Node());
		al.add(new Node());
	}
	
	
	public static void main(String[] args) {
		
		Lambda l = new Lambda();
		try{				
			l.al.forEach( n ->
				System.out.println(n.a[2]*n.a[3])
				);
		} catch (java.lang.NullPointerException e) {
			System.out.println(e);
		}
		
		
	}

}

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when i ran above code i got below exception.
please advise
java.lang.NullPointerException
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