超高效率的处理 两个集合
一种是for循环方式，一种是 stream 方式；在处理数据量很大是会相差上千倍。
处理数据量大时，使用stream 方式，很小的数据用for就可以；
处理100000条数据处理结果：
处理100条数据处理结果：
示例代码：kotlin
import java.util.* import java.util.stream.Collectors import kotlin.collections.ArrayList class Test { companion object { private var i0 = 0 private var i02 = 0 private var i1 = 0 @JvmStatic fun main(args: Array<String>) { println("---------START---------") val i=99999 // val i = 99 val r = Random() val sList = ArrayList<String>() for (i in 0..i) { sList.add(java.lang.String.valueOf(r.nextInt(500000) + 1)) } val cList = ArrayList<String>() for (i in 0..i) { cList.add((i + 1).toString()) } val s1 = System.currentTimeMillis() doubleForMethod(sList, cList) val e1 = System.currentTimeMillis() println("FOR--->" + (e1 - s1) + "ms ---->" + i0) val s2 = System.currentTimeMillis() streamMethod(sList, cList) val e2 = System.currentTimeMillis() println("STREAM--->" + (e2 - s2) + "ms ---->" + i1) val s3 = System.currentTimeMillis() doubleForMethod2(sList, cList) val e3 = System.currentTimeMillis() println("FOR 2 --->" + (e3 - s3) + "ms ---->" + i02) println("----------END--------") } private fun streamMethod(sList: List<String>, aList: List<String>) { // 把班级列表转成map，那么班级id就是唯一的id val noClassMap: Map<String, String> = aList.stream().collect(Collectors.toMap({ t -> t }) { t -> t }) sList.stream().forEach { h: String -> if (noClassMap.containsKey(h)) { i1++ } } } // for双层循环的方式 private fun doubleForMethod(sList: List<String>, aList: List<String>) { for (i in sList.indices) { val student = sList[i] for (j in aList.indices) { val noClass = aList[j] if (student == noClass) { i0++ } } } } // for双层循环的方式 private fun doubleForMethod2(sList: List<String>, aList: List<String>) { sList.forEach { if (aList.contains(it)) { i02++ } } } } }
示例代码：Java
public class Run { private static int i0=0; private static int i1=0; public static void main(String[] args) { Random r = new Random(); ArrayList sList = new ArrayList<String>(); for (int i = 0; i < 100000; i++) { sList.add(String.valueOf(r.nextInt(500000) + 1)); } ArrayList cList = new ArrayList<String>(); for (int i = 0; i < 100000; i++) { cList.add(String.valueOf(i + 1)); } long s1 = System.currentTimeMillis(); doubleForMethod(sList, cList); long e1 = System.currentTimeMillis(); System.out.println("FOR--->" + (e1 - s1) + "---->" + i0); long s2 = System.currentTimeMillis(); streamMethod(sList, cList); long e2 = System.currentTimeMillis(); System.out.println("STREAM--->" + (e2 - s2) + "---->" + i1); ） // for双层循环的方式 private static void doubleForMethod(List<String> sList, List<String> fList) { for (int i = 0; i < sList.size(); i++) { String student = sList.get(i); for (int j = 0; j < fList.size(); j++) { String noClass = fList.get(j); if (student.equals(noClass)) { i0++; } } } } private static void streamMethod(List<String> sList, List<String> fList) { // 把班级列表转成map，那么班级id就是唯一的id Map<String, String> noClassMap = fList.stream().collect(Collectors.toMap(t -> t, t -> t)); sList.stream().forEach(h -> { if (noClassMap.containsKey(h)) { i1++; } }); } }
