JAVA stream常用语法(不定期更新)

JAVA stream常用语法常用语法基本数据类型集合操作自定义对象类型集合操作测试类对象实体类总结常用语法基本数据类型集合操作publicstaticvoidmain(String[]args)throwsClassNotFoundException,NoSuchMethodException{setArrayList();setIntArrayList();//获取长度longcountlist.stream().count();System.out.println(countcount);System.out.println(去重);//去重list.stream().distinct().forEach(p-System.out.println((p)));System.out.println(获取前2个);list.stream().limit(2).forEach(p-System.out.println((p)));System.out.println(获取两位数);list.stream().filter(p-p.toString().length()2).forEach(p-System.out.println(p));System.out.println(跳过前四个);list.stream().skip(4).forEach(p-System.out.println((p)));System.out.println(排序);list.stream().sorted(Comparator.comparing(Student::getAge).reversed()).forEach(p-System.out.println(p.getAge()));System.out.println(0~11最小);intaintList.stream().reduce(Integer::min).get();System.out.println(0~11最小a);System.out.println(0~11最大);intbintList.stream().reduce(Integer::max).get();System.out.println(0~11最大b);}publicstaticvoidsetIntArrayList(){for(inti11;i0;i--){intList.add(i);}}publicstaticvoidsetArrayList(){for(inti11;i0;i--){StudentstunewStudent();stu.setAge(i);stu.setName(qwqwi);stu.setNumber(Double.parseDouble(i.i));list.add(stu);}}自定义对象类型集合操作测试类publicstaticvoidmain(String[]args)throwsClassNotFoundException,NoSuchMethodException{//测试转换//获取到传来的json字符串StudentstunewStudent();ListStudentstudentsnewArrayList();stu.setAge(10);stu.setName(name1);stu.setNumber(10.00);students.add(stu);stunewStudent();stu.setAge(11);stu.setName(name2);stu.setNumber(11.00);students.add(stu);stunewStudent();stu.setAge(13);stu.setName(name2);stu.setNumber(13.00);students.add(stu);stunewStudent();stu.setAge(12);stu.setName(name3);stu.setNumber(12.00);students.add(stu);// 返回Map(以名字为Key单个对象为Value如果有多个对象名字相同只将第一次取到的值作为Value)MapString,StudentstudentMapstudents.stream().collect(Collectors.toMap(Student::getName,item-item,(v1,v2)-v1));System.out.println(---- 名字分组结果,单一studentMap);// 返回Map(以名字为Keynumber累加为Value如果有多个对象名字相同将每个对象的number累加)MapString,IntegerstudentNameNumberMapstudents.stream().collect(Collectors.toMap(Student::getName,Student::getAge,(v1,v2)-v1v2));System.out.println(---- 名字分组结果,value累加studentNameNumberMap);// 返回对象列表中指定属性的list列表ListIntegerageListstudents.stream().map(Student::getAge).collect(Collectors.toList());// 年龄列表[10, 11, 13, 12]System.out.println(年龄列表ageList);// 返回Map(以名称为Key集合对象为Value)MapString,ListStudentmapstudents.stream().collect(Collectors.groupingBy(Student::getName));// 分组结果{name3[Student{namename3, age12, number12.0}], name2[Student{namename2, age11, number11.0}, Student{namename2, age13, number13.0}], name1[Student{namename1, age10, number10.0}]}System.out.println(分组结果map);// 返回Map(以年龄为Key名称为Value)MapInteger,Stringmap2students.stream().collect(Collectors.toMap(Student::getAge,Student::getName));// 分组结果2{10name1, 11name2, 12name3, 13name2}System.out.println(分组结果2map2);//返回Map(以年龄为Key对象为Value)MapInteger,Studentmap3students.stream().collect(Collectors.toMap(Student::getAge,item-item));// 分组结果3{10Student{namename1, age10, number10.0}, 11Student{namename2, age11, number11.0}, 12Student{namename3, age12, number12.0}, 13Student{namename2, age13, number13.0}}System.out.println(分组结果3map3);finalbooleanisBigTenstudents.stream().allMatch(p-p.getAge()10);// 年龄是否都大于10falseSystem.out.println(年龄是否都大于10isBigTen);// 求年龄之和LongSummaryStatisticssummaryObjectstudents.stream().collect(Collectors.summarizingLong(Student::getAge));// 年龄之和LongSummaryStatistics{count4, sum46, min10, average11.500000, max13}System.out.println(年龄之和summaryObject);OptionalIntegersumOpstudents.stream().map(Student::getAge).reduce(Integer::sum);// 年龄总和Optional[46]System.out.println(年龄总和sumOp);OptionalIntegerminOpstudents.stream().map(Student::getAge).reduce(Integer::min);// 最小年龄Optional[10]System.out.println(最小年龄minOp);OptionalIntegermaxOpstudents.stream().map(Student::getAge).reduce(Integer::max);IntegeropopmaxOp.orElse(0);// 最大年龄13System.out.println(最大年龄opop);// 计算平均值finalDoubledoubleAveragestudents.stream().collect(Collectors.averagingDouble(p-p.getNumber()));// 金额平均值11.5System.out.println(金额平均值doubleAverage);finalDoubleintAveragestudents.stream().collect(Collectors.averagingInt(p-p.getAge()));// 年龄平均值11.5System.out.println(年龄平均值intAverage);ListStudentlalstudents.stream().map((p)-{StudentstnewStudent();st.setName(namep.getAge());returnst;}).distinct().collect(Collectors.toList());// 去重后的名字年龄数组[Student{namename10, age0, number0.0}, Student{namename11, age0, number0.0}, Student{namename13, age0, number0.0}, Student{namename12, age0, number0.0}]System.out.println(去重后的名字年龄数组lal.toString());ListStudentqqwstudents.stream().map((p)-{p.setName(p.getName().toUpperCase());returnp;}).collect(Collectors.toList());// 去重后的名字大写数组[Student{nameNAME1, age10, number10.0}, Student{nameNAME2, age11, number11.0}, Student{nameNAME2, age13, number13.0}, Student{nameNAME3, age12, number12.0}]System.out.println(去重后的名字大写数组qqw);}对象实体类publicclassStudent{publicStringname;publicintage;publicdoublenumber;publicStringgetName(){returnname;}publicvoidsetName(Stringname){this.namename;}publicintgetAge(){returnage;}publicvoidsetAge(intage){this.ageage;}publicdoublegetNumber(){returnnumber;}publicvoidsetNumber(doublenumber){this.numbernumber;}OverridepublicStringtoString(){returnStudent{namename\, ageage, numbernumber};}}总结通过个人对stream和for的性能比较stream性能一直较差但是相差不大。对于简洁逻辑的集合操作stream操作代码量比for循环代码量简洁。stream语法较复杂易读性较差简单的集合元素操作逻辑推荐使用stream操作但是如果操作逻辑复杂还是推荐使用for操作易读好维护。