Java 8 Stream

Java8Tester.java 檔案

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: “);

// 計算空字串
List<String> strings = Arrays.asList(“abc”, “”, “bc”, “efg”, “abcd”,””, “jkl”);
System.out.println(“列表: ” +strings);
long count = getCountEmptyStringUsingJava7(strings);

System.out.println(“空字元數量為: ” + count);
count = getCountLength3UsingJava7(strings);

System.out.println(“字串長度為 3 的數量為: ” + count);

// 刪除空字串
List<String> filtered = deleteEmptyStringsUsingJava7(strings);
System.out.println(“篩選後的列表: ” + filtered);

// 刪除空字串，並使用逗號把它們合併起來
String mergedString = getMergedStringUsingJava7(strings,”, “);
System.out.println(“合併字串: ” + mergedString);
List<Integer> numbers = Arrays.asList(3, 2, 2, 3, 7, 3, 5);

// 獲取列表元素平方數
List<Integer> squaresList = getSquares(numbers);
System.out.println(“平方數列表: ” + squaresList);
List<Integer> integers = Arrays.asList(1,2,13,4,15,6,17,8,19);

System.out.println(“列表: ” +integers);
System.out.println(“列表中最大的數 : ” + getMax(integers));
System.out.println(“列表中最小的數 : ” + getMin(integers));
System.out.println(“所有數之和 : ” + getSum(integers));
System.out.println(“平均數 : ” + getAverage(integers));
System.out.println(“隨機數: “);

// 輸出10個隨機數
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(“空字串數量為: ” + count);

count = strings.stream().filter(string -> string.length() == 3).count();
System.out.println(“字串長度為 3 的數量為: ” + count);

filtered = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.toList());
System.out.println(“篩選後的列表: ” + filtered);

mergedString = strings.stream().filter(string ->!string.isEmpty()).collect(Collectors.joining(“, “));
System.out.println(“合併字串: ” + 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(“列表中最大的數 : ” + stats.getMax());
System.out.println(“列表中最小的數 : ” + stats.getMin());
System.out.println(“所有數之和 : ” + stats.getSum());
System.out.println(“平均數 : ” + stats.getAverage());
System.out.println(“隨機數: “);

random.ints().limit(10).sorted().forEach(System.out::println);

// 並行處理
count = strings.parallelStream().filter(string -> string.isEmpty()).count();
System.out.println(“空字串的數量為: ” + 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();
}
}