1. A List of Strings to Uppercase

1.1 Simple Java example to convert a list of Strings to upper case.

package com.mkyong.java8;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class TestJava8 {

    public static void main(String[] args) {

        List<String> alpha = Arrays.asList("a", "b", "c", "d");

        //Before Java8

        List<String> alphaUpper = new ArrayList<>();

        for (String s : alpha) {

            alphaUpper.add(s.toUpperCase());

        }

        System.out.println(alpha); //[a, b, c, d]

        System.out.println(alphaUpper); //[A, B, C, D]

        // Java 8

        List<String> collect = alpha.stream().map(String::toUpperCase).collect(Collectors.toList());

        System.out.println(collect); //[A, B, C, D]

        // Extra, streams apply to any data type.

        List<Integer> num = Arrays.asList(1,2,3,4,5);

        List<Integer> collect1 = num.stream().map(n -> n * 2).collect(Collectors.toList());

        System.out.println(collect1); //[2, 4, 6, 8, 10]

    }

}

2. List of objects -> List of String

2.1 Get all the name values from a list of the staff objects.

package com.mkyong.java8;

import java.math.BigDecimal;

public class Staff {

    private String name;

    private int age;

    private BigDecimal salary;

	//...

}

package com.mkyong.java8;

import java.math.BigDecimal;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class TestJava8 {

    public static void main(String[] args) {

        List<Staff> staff = Arrays.asList(

                new Staff("mkyong", 30, new BigDecimal(10000)),

                new Staff("jack", 27, new BigDecimal(20000)),

                new Staff("lawrence", 33, new BigDecimal(30000))

        );

        //Before Java 8

        List<String> result = new ArrayList<>();

        for (Staff x : staff) {

            result.add(x.getName());

        }

        System.out.println(result); //[mkyong, jack, lawrence]

        //Java 8

        List<String> collect = staff.stream().map(x -> x.getName()).collect(Collectors.toList());

        System.out.println(collect); //[mkyong, jack, lawrence]

    }

}

3. List of objects -> List of other objects

3.1 This example shows you how to convert a list of staff objects into a list of StaffPublic objects.

package com.mkyong.java8;

import java.math.BigDecimal;

public class Staff {

    private String name;

    private int age;

    private BigDecimal salary;

	//...

}

package com.mkyong.java8;

public class StaffPublic {

    private String name;

    private int age;

    private String extra;

    //...

}

3.2 Before Java 8.

package com.mkyong.java8;

import java.math.BigDecimal;

import java.util.ArrayList;

import java.util.Arrays;

import java.util.List;

public class BeforeJava8 {

    public static void main(String[] args) {

        List<Staff> staff = Arrays.asList(

                new Staff("mkyong", 30, new BigDecimal(10000)),

                new Staff("jack", 27, new BigDecimal(20000)),

                new Staff("lawrence", 33, new BigDecimal(30000))

        );

        List<StaffPublic> result = convertToStaffPublic(staff);

        System.out.println(result);

    }

    private static List<StaffPublic> convertToStaffPublic(List<Staff> staff) {

        List<StaffPublic> result = new ArrayList<>();

        for (Staff temp : staff) {

            StaffPublic obj = new StaffPublic();

            obj.setName(temp.getName());

            obj.setAge(temp.getAge());

            if ("mkyong".equals(temp.getName())) {

                obj.setExtra("this field is for mkyong only!");

            }

            result.add(obj);

        }

        return result;

    }

}

Output

[

	StaffPublic{name='mkyong', age=30, extra='this field is for mkyong only!'},

	StaffPublic{name='jack', age=27, extra='null'},

	StaffPublic{name='lawrence', age=33, extra='null'}

]

3.3 Java 8 example.

package com.mkyong.java8;

package com.hostingcompass.web.java8;

import java.math.BigDecimal;

import java.util.Arrays;

import java.util.List;

import java.util.stream.Collectors;

public class NowJava8 {

    public static void main(String[] args) {

        List<Staff> staff = Arrays.asList(

                new Staff("mkyong", 30, new BigDecimal(10000)),

                new Staff("jack", 27, new BigDecimal(20000)),

                new Staff("lawrence", 33, new BigDecimal(30000))

        );

		// convert inside the map() method directly.

        List<StaffPublic> result = staff.stream().map(temp -> {

            StaffPublic obj = new StaffPublic();

            obj.setName(temp.getName());

            obj.setAge(temp.getAge());

            if ("mkyong".equals(temp.getName())) {

                obj.setExtra("this field is for mkyong only!");

            }

            return obj;

        }).collect(Collectors.toList());

        System.out.println(result);

    }

}

Output

[

	StaffPublic{name='mkyong', age=30, extra='this field is for mkyong only!'},

	StaffPublic{name='jack', age=27, extra='null'},

	StaffPublic{name='lawrence', age=33, extra='null'}

]

http://www.mkyong.com/java8/java-8-streams-map-examples/