Java 8 Stream

Java8Tester.java 文件

package org.java.base.stream; import java.util.ArrayList; import java.util.Arrays; import java.util.IntSummaryStatistics; import java.util.List; import java.util.Random; import java.util.stream.Collectors; import java.util.Map;
public class Java8Tester { public static void main(String args[]){ System.out.println(“使用 Java 7: “);
// 计算空字符串 List<String> strings = Arrays.asList(“abc”, “”, “bc”, “efg”, “abcd”,””, “jkl”); System.out.println(“列表: ” +strings); long count = getCountEmptyStringUsingJava7(strings);
System.out.println(“空字符数量为: ” + count); count = getCountLength3UsingJava7(strings);
System.out.println(“字符串长度为 3 的数量为: ” + count);
// 删除空字符串 List<String> filtered = deleteEmptyStringsUsingJava7(strings); System.out.println(“筛选后的列表: ” + filtered);
// 删除空字符串，并使用逗号把它们合并起来 String mergedString = getMergedStringUsingJava7(strings,”, “); System.out.println(“合并字符串: ” + mergedString); List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);
// 获取列表元素平方数 List<Integer> squaresList = getSquares(numbers); System.out.println(“平方数列表: ” + squaresList); List<Integer> integers = Arrays.asList(1,2,13,4,15,6,17,8,19);
System.out.println(“列表: ” +integers); System.out.println(“列表中最大的数 : ” + getMax(integers)); System.out.println(“列表中最小的数 : ” + getMin(integers)); System.out.println(“所有数之和 : ” + getSum(integers)); System.out.println(“平均数 : ” + getAverage(integers)); System.out.println(“随机数: “);
// 输出10个随机数 Random random = new Random();
for(int i=0; i < 10; i++){ System.out.println(random.nextInt()); }
System.out.println(“使用 Java 8: “); System.out.println(“列表: ” +strings);
count = strings.stream().filter(string->string.isEmpty()).count(); System.out.println(“空字符串数量为: ” + count);
count = strings.stream().filter(string -> string.length() == 3).count(); System.out.println(“字符串长度为 3 的数量为: ” + count);
filtered = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.toList()); System.out.println(“筛选后的列表: ” + filtered);
mergedString = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.joining(“, “)); System.out.println(“合并字符串: ” + mergedString);
squaresList = numbers.stream().map( i ->i*i).distinct().collect(Collectors.toList()); System.out.println(“Squares List: ” + squaresList); System.out.println(“列表: ” +integers);
IntSummaryStatistics stats = integers.stream().mapToInt((x) ->x).summaryStatistics();
System.out.println(“列表中最大的数 : ” + stats.getMax()); System.out.println(“列表中最小的数 : ” + stats.getMin()); System.out.println(“所有数之和 : ” + stats.getSum()); System.out.println(“平均数 : ” + stats.getAverage()); System.out.println(“随机数: “);
random.ints().limit(10).sorted().forEach(System.out::println);
// 并行处理 count = strings.parallelStream().filter(string -> string.isEmpty()).count(); System.out.println(“空字符串的数量为: ” + count); }
private static int getCountEmptyStringUsingJava7(List<String> strings){ int count = 0;
for(String string: strings){
if(string.isEmpty()){ count++; } } return count; }
private static int getCountLength3UsingJava7(List<String> strings){ int count = 0;
for(String string: strings){
if(string.length() == 3){ count++; } } return count; }
private static List<String> deleteEmptyStringsUsingJava7(List<String> strings){ List<String> filteredList = new ArrayList<String>();
for(String string: strings){
if(!string.isEmpty()){ filteredList.add(string); } } return filteredList; }
private static String getMergedStringUsingJava7(List<String> strings, String separator){ StringBuilder stringBuilder = new StringBuilder();
for(String string: strings){
if(!string.isEmpty()){ stringBuilder.append(string); stringBuilder.append(separator); } } String mergedString = stringBuilder.toString(); return mergedString.substring(0, mergedString.length()-2); }
private static List<Integer> getSquares(List<Integer> numbers){ List<Integer> squaresList = new ArrayList<Integer>();
for(Integer number: numbers){ Integer square = new Integer(number.intValue() * number.intValue());
if(!squaresList.contains(square)){ squaresList.add(square); } } return squaresList; }
private static int getMax(List<Integer> numbers){ int max = numbers.get(0);
for(int i=1;i < numbers.size();i++){
Integer number = numbers.get(i);
if(number.intValue() > max){ max = number.intValue(); } } return max; }
private static int getMin(List<Integer> numbers){ int min = numbers.get(0);
for(int i=1;i < numbers.size();i++){ Integer number = numbers.get(i);
if(number.intValue() < min){ min = number.intValue(); } } return min; }
private static int getSum(List numbers){ int sum = (int)(numbers.get(0));
for(int i=1;i < numbers.size();i++){ sum += (int)numbers.get(i); } return sum; }
private static int getAverage(List<Integer> numbers){ return getSum(numbers) / numbers.size(); } }