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今天就跟大家聊聊有關(guān) Java8中怎么操作Stream 對(duì)集合，可能很多人都不太了解，為了讓大家更加了解，小編給大家總結(jié)了以下內(nèi)容，希望大家根據(jù)這篇文章可以有所收獲。
首先為了說明Stream對(duì)對(duì)象集合的操作，新建一個(gè)Student類（學(xué)生類）,覆寫了equals()和hashCode()方法
public class Student {
private Long id;
private String name;
private int age;
private String address;
public Student() {}
public Student(Long id, String name, int age, String address) {
this.id = id;
this.name = name;
this.age = age;
this.address = address;
}
@Override
public String toString() {
return "Student{" +
"id=" + id +
", name='" + name + '\'' +
", age=" + age +
", address='" + address + '\'' +
'}';
}
@Override
public boolean equals(Object o) {
if (this == o) return true;
if (o == null || getClass() != o.getClass()) return false;
Student student = (Student) o;
return age == student.age &&
Objects.equals(id, student.id) &&
Objects.equals(name, student.name) &&
Objects.equals(address, student.address);
}
@Override
public int hashCode() {
return Objects.hash(id, name, age, address);
}
public Long getId() {
return id;
}
public void setId(Long id) {
this.id = id;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
}public static void main(String [] args) {
Student s1 = new Student(1L, "肖戰(zhàn)", 15, "浙江");
Student s2 = new Student(2L, "王一博", 15, "湖北");
Student s3 = new Student(3L, "楊紫", 17, "北京");
Student s4 = new Student(4L, "李現(xiàn)", 17, "浙江");
List<Student> students = new ArrayList<>();
students.add(s1);
students.add(s2);
students.add(s3);
students.add(s4);
List<Student> streamStudents = testFilter(students);
streamStudents.forEach(System.out::println);
}
/**
* 集合的篩選
* @param students
* @return
*/
private static List<Student> testFilter(List<Student> students) {
//篩選年齡大于15歲的學(xué)生
// return students.stream().filter(s -> s.getAge()>15).collect(Collectors.toList());
//篩選住在浙江省的學(xué)生
return students.stream().filter(s ->"浙江".equals(s.getAddress())).collect(Collectors.toList());
}運(yùn)行結(jié)果：
這里我們創(chuàng)建了四個(gè)學(xué)生，經(jīng)過filter的篩選，篩選出地址是浙江的學(xué)生集合。
public static void main(String [] args) {
Student s1 = new Student(1L, "肖戰(zhàn)", 15, "浙江");
Student s2 = new Student(2L, "王一博", 15, "湖北");
Student s3 = new Student(3L, "楊紫", 17, "北京");
Student s4 = new Student(4L, "李現(xiàn)", 17, "浙江");
List<Student> students = new ArrayList<>();
students.add(s1);
students.add(s2);
students.add(s3);
students.add(s4);
testMap(students);
}
/**
* 集合轉(zhuǎn)換
* @param students
* @return
*/
private static void testMap(List<Student> students) {
//在地址前面加上部分信息，只獲取地址輸出
List<String> addresses = students.stream().map(s ->"住址:"+s.getAddress()).collect(Collectors.toList());
addresses.forEach(a ->System.out.println(a));
}運(yùn)行結(jié)果
map就是將對(duì)應(yīng)的元素按照給定的方法進(jìn)行轉(zhuǎn)換。
public static void main(String [] args) {
testDistinct1();
}
/**
* 集合去重（基本類型）
*/
private static void testDistinct1() {
//簡(jiǎn)單字符串的去重
List<String> list = Arrays.asList("111","222","333","111","222");
list.stream().distinct().forEach(System.out::println);
}運(yùn)行結(jié)果：
public static void main(String [] args) {
testDistinct2();
}
/**
* 集合去重（引用對(duì)象）
*/
private static void testDistinct2() {
//引用對(duì)象的去重，引用對(duì)象要實(shí)現(xiàn)hashCode和equal方法，否則去重?zé)o效
Student s1 = new Student(1L, "肖戰(zhàn)", 15, "浙江");
Student s2 = new Student(2L, "王一博", 15, "湖北");
Student s3 = new Student(3L, "楊紫", 17, "北京");
Student s4 = new Student(4L, "李現(xiàn)", 17, "浙江");
Student s5 = new Student(1L, "肖戰(zhàn)", 15, "浙江");
List<Student> students = new ArrayList<>();
students.add(s1);
students.add(s2);
students.add(s3);
students.add(s4);
students.add(s5);
students.stream().distinct().forEach(System.out::println);
}運(yùn)行結(jié)果：
可以看出，兩個(gè)重復(fù)的“肖戰(zhàn)”同學(xué)進(jìn)行了去重，這不僅因?yàn)槭褂昧薲istinct()方法，而且因?yàn)镾tudent對(duì)象重寫了equals和hashCode()方法，否則去重是無效的。
public static void main(String [] args) {
testSort1();
}
/**
* 集合排序（默認(rèn)排序）
*/
private static void testSort1() {
List<String> list = Arrays.asList("333","222","111");
list.stream().sorted().forEach(System.out::println);
}運(yùn)行結(jié)果：
public static void main(String [] args) {
testSort2();
}
/**
* 集合排序（指定排序規(guī)則）
*/
private static void testSort2() {
Student s1 = new Student(1L, "肖戰(zhàn)", 15, "浙江");
Student s2 = new Student(2L, "王一博", 15, "湖北");
Student s3 = new Student(3L, "楊紫", 17, "北京");
Student s4 = new Student(4L, "李現(xiàn)", 17, "浙江");
List<Student> students = new ArrayList<>();
students.add(s1);
students.add(s2);
students.add(s3);
students.add(s4);
students.stream()
.sorted((stu1,stu2) ->Long.compare(stu2.getId(), stu1.getId()))
.sorted((stu1,stu2) -> Integer.compare(stu2.getAge(),stu1.getAge()))
.forEach(System.out::println);
}運(yùn)行結(jié)果：
上面指定排序規(guī)則，先按照學(xué)生的id進(jìn)行降序排序，再按照年齡進(jìn)行降序排序
public static void main(String [] args) {
testLimit();
}
/**
* 集合limit，返回前幾個(gè)元素
*/
private static void testLimit() {
List<String> list = Arrays.asList("333","222","111");
list.stream().limit(2).forEach(System.out::println);
}運(yùn)行結(jié)果：
public static void main(String [] args) {
testSkip();
}
/**
* 集合skip，刪除前n個(gè)元素
*/
private static void testSkip() {
List<String> list = Arrays.asList("333","222","111");
list.stream().skip(2).forEach(System.out::println);
}運(yùn)行結(jié)果：
public static void main(String [] args) {
testReduce();
}
/**
* 集合reduce,將集合中每個(gè)元素聚合成一條數(shù)據(jù)
*/
private static void testReduce() {
List<String> list = Arrays.asList("歡","迎","你");
String appendStr = list.stream().reduce("北京",(a,b) -> a+b);
System.out.println(appendStr);
}運(yùn)行結(jié)果：
public static void main(String [] args) {
testMin();
}
/**
* 求集合中元素的最小值
*/
private static void testMin() {
Student s1 = new Student(1L, "肖戰(zhàn)", 14, "浙江");
Student s2 = new Student(2L, "王一博", 15, "湖北");
Student s3 = new Student(3L, "楊紫", 17, "北京");
Student s4 = new Student(4L, "李現(xiàn)", 17, "浙江");
List<Student> students = new ArrayList<>();
students.add(s1);
students.add(s2);
students.add(s3);
students.add(s4);
Student minS = students.stream().min((stu1,stu2) ->Integer.compare(stu1.getAge(),stu2.getAge())).get();
System.out.println(minS.toString());
}運(yùn)行結(jié)果：
上面是求所有學(xué)生中年齡最小的一個(gè)，max同理，求最大值。
public static void main(String [] args) {
testMatch();
}
private static void testMatch() {
Student s1 = new Student(1L, "肖戰(zhàn)", 15, "浙江");
Student s2 = new Student(2L, "王一博", 15, "湖北");
Student s3 = new Student(3L, "楊紫", 17, "北京");
Student s4 = new Student(4L, "李現(xiàn)", 17, "浙江");
List<Student> students = new ArrayList<>();
students.add(s1);
students.add(s2);
students.add(s3);
students.add(s4);
Boolean anyMatch = students.stream().anyMatch(s ->"湖北".equals(s.getAddress()));
if (anyMatch) {
System.out.println("有湖北人");
}
Boolean allMatch = students.stream().allMatch(s -> s.getAge()>=15);
if (allMatch) {
System.out.println("所有學(xué)生都滿15周歲");
}
Boolean noneMatch = students.stream().noneMatch(s -> "楊洋".equals(s.getName()));
if (noneMatch) {
System.out.println("沒有叫楊洋的同學(xué)");
}
}看完上述內(nèi)容，你們對(duì) Java8中怎么操作Stream 對(duì)集合有進(jìn)一步的了解嗎？如果還想了解更多知識(shí)或者相關(guān)內(nèi)容，請(qǐng)關(guān)注億速云行業(yè)資訊頻道，感謝大家的支持。
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