在Java 8中stream().map()，您可以将对象转换为其他对象。查看以下示例：

1.大写字符串列表

1.1简单的Java示例将Strings列表转换为大写。

TestJava8.javapackage 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
     
       alpha = Arrays.asList("a", "b", "c", "d");        //Before Java8        List
      
        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
       
         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
        
          num = Arrays.asList(1,2,3,4,5);        List
         
           collect1 = num.stream().map(n -> n * 2).collect(Collectors.toList());        System.out.println(collect1); //[2, 4, 6, 8, 10]    }}
         
        
       
      
     

　　

 

2.对象列表 - >字符串列表

2.1 name从staff对象列表中获取所有值。

Staff.javapackage com.mkyong.java8;import java.math.BigDecimal;public class Staff {    private String name;    private int age;    private BigDecimal salary;    //...}TestJava8.javapackage 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 = 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
      
        result = new ArrayList<>();        for (Staff x : staff) {            result.add(x.getName());        }        System.out.println(result); //[mkyong, jack, lawrence]        //Java 8        List
       
         collect = staff.stream().map(x -> x.getName()).collect(Collectors.toList());        System.out.println(collect); //[mkyong, jack, lawrence]    }}
       
      
     

　　

 

对象列表 - >其他对象列表

3.1此示例说明如何将staff对象列表转换为对象列表StaffPublic。

Staff.javapackage com.mkyong.java8;import java.math.BigDecimal;public class Staff {    private String name;    private int age;    private BigDecimal salary;    //...}StaffPublic.javapackage com.mkyong.java8;public class StaffPublic {    private String name;    private int age;    private String extra;    //...}

 

 

3.2 Java 8之前。

BeforeJava8.javapackage 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 = Arrays.asList(                new Staff("mkyong", 30, new BigDecimal(10000)),                new Staff("jack", 27, new BigDecimal(20000)),                new Staff("lawrence", 33, new BigDecimal(30000))        );        List
      
        result = convertToStaffPublic(staff);        System.out.println(result);    }    private static List
       
         convertToStaffPublic(List
        
          staff) {        List
         
           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;    }}输出[    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的例子。

NowJava8.java

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 = 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
      
        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);    }}
      
     

 

 

输出

[    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'} ]