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.java
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.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.java
package com.mkyong.java8;
import java.math.BigDecimal;
public class Staff {
private String name;
private int age;
private BigDecimal salary;
//...
}
TestJava8.java
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. 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.java
package com.mkyong.java8;
import java.math.BigDecimal;
public class Staff {
private String name;
private int age;
private BigDecimal salary;
//...
}
StaffPublic.java
package com.mkyong.java8;
public class StaffPublic {
private String name;
private int age;
private String extra;
//...
}
3.2 Java 8之前
BeforeJava8.java
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; } }
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> 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); } }
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'}
]