JAVA EE: How to convert lower alpha list to upper alpha list using Java 8 streams

Thursday 31 August 2017

How to convert lower alpha list to upper alpha list using Java 8 streams | Streams in Java 8

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NonStreamDemo.java

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;

public class NonStreamDemo
{
    public static void main(String[] args)
    {

        List<String> lowerAlphaList = Arrays.asList("a", "b", "c ");
        System.out.println("lowerAlphaList = "+lowerAlphaList); // [a, b, c, d]

        // Before Java8
        List<String> upperAlphaList = new ArrayList<>();
        for (String str : lowerAlphaList)
        {
            upperAlphaList.add(str.toUpperCase());
        }

        System.out.println("upperAlphaList = "+upperAlphaList); // [A, B, C, D]

    }

}

Output

lowerAlphaList = [a, b, c ]
upperAlphaList = [A, B, C ]

StreamDemo1.java

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class StreamDemo1
{
    public static void main(String[] args)
    {

        List<String> lowerAlphaList = Arrays.asList("a", "b", "c ");
        System.out.println("lowerAlphaList = "+lowerAlphaList); // [a, b, c, d]
        // Java 8
        List<String> upperAlphaList = lowerAlphaList.stream().map(String::toUpperCase)
                                                             .collect(Collectors.toList());
        System.out.println("upperAlphaList = "+upperAlphaList); // [A, B, C, D]     
        
    }

}

Output

lowerAlphaList = [a, b, c ]
upperAlphaList = [A, B, C ]

StreamDemo2.java

import java.util.Arrays;
import java.util.List;
import java.util.stream.Collectors;

public class StreamDemo2
{
    public static void main(String[] args)
    {

        // streams apply to any data type.
        List<Integer> numberList = Arrays.asList(1, 2, 3, 4, 5);
        
        List<Integer> resultList = numberList.stream().map(n -> n * 2)
                                               .collect(Collectors.toList());
        
        System.out.println(resultList); // [2, 4, 6, 8, 10]
    }

}