Stream 完整实例

布满荆棘的人生 2023-10-06 08:33 15阅读 0赞

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![在这里插入图片描述][20200511182504697.png]

### Stream 完整实例 ###

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();
       }
    }

执行的脚本:

$ javac Java8Tester.java 
    $ java Java8Tester
    使用 Java 7: 
    列表: [abc, , bc, efg, abcd, , jkl]
    空字符数量为: 2
    字符串长度为 3 的数量为: 3
    筛选后的列表: [abc, bc, efg, abcd, jkl]
    合并字符串: abc, bc, efg, abcd, jkl
    平方数列表: [9, 4, 49, 25]
    列表: [1, 2, 13, 4, 15, 6, 17, 8, 19]
    列表中最大的数 : 19
    列表中最小的数 : 1
    所有数之和 : 85
    平均数 : 9
    随机数: 
    -393170844
    -963842252
    447036679
    -1043163142
    -881079698
    221586850
    -1101570113
    576190039
    -1045184578
    1647841045
    使用 Java 8: 
    列表: [abc, , bc, efg, abcd, , jkl]
    空字符串数量为: 2
    字符串长度为 3 的数量为: 3
    筛选后的列表: [abc, bc, efg, abcd, jkl]
    合并字符串: abc, bc, efg, abcd, jkl
    Squares List: [9, 4, 49, 25]
    列表: [1, 2, 13, 4, 15, 6, 17, 8, 19]
    列表中最大的数 : 19
    列表中最小的数 : 1
    所有数之和 : 85
    平均数 : 9.444444444444445
    随机数: 
    -1743813696
    -1301974944
    -1299484995
    -779981186
    136544902
    555792023
    1243315896
    1264920849
    1472077135
    1706423674
    空字符串的数量为: 2

[Link 1]: https://www.runoob.com/java/java8-streams.html
[20200511182504697.png]: https://img-blog.csdnimg.cn/20200511182504697.png