J2SE 8的流库 --- 转换流, 得到的还是流
2024-10-14 01:41:23
流的转换, 按照条件过滤/映射/摊平/截取/丢弃/连接/去重/排序。
辅助方法
public static int myCompare(String x, String y) {
if(x.length()>y.length()){
return 1;
}else if(x.length()==y.length()){
return x.compareTo(y);
}else{
return -1;
}
}
private static Stream<Integer> letters(String s){
return s.chars().boxed(); //将所有的chars抽成流
}
public static <T> void show(String title, Stream<T> stream){
System.out.println("title:"+title);
List<T> collect = stream.limit(10).collect(Collectors.toList());
collect.forEach(n->System.out.println(n));
System.out.println();
}
//????
@SuppressWarnings("unchecked")
public static <T extends Stream<?>> void deepShow(String title, T stream){
System.out.println("title:"+title);
stream.forEach(n->{
if(n instanceof Stream){
deepShow(title, (T)n);
}else{
System.out.println(n);
}
});
System.out.println();
}1. 过滤 filter() Predicate<? super T> predicate T->boolean 按照特定条件过滤
Stream<String> filterStream = arrayList.stream().filter((w)->(w.length()>2));
show("filterStream", filterStream);2. 映射 map() Function<? super T, ? extends R> mapper T->R 按照特定方式转换
Stream<String> mapStream = arrayList.stream().map(String::toUpperCase);
show("mapStream", mapStream);3. 摊平 flatMap() 包含流的流 摊平
Stream<Stream<Integer>> flatStream = arrayList.stream().map(w->letters(w));
deepShow("flatStream", flatStream);
//==>摊平
Stream<Integer> flatMapStream = arrayList.stream().flatMap(w->letters(w));
flatMapStream.forEach(n->System.out.println((char)(int)n));
System.out.println();4. 截取 limit(n) 在n个元素后结束
Stream<String> limitStream = arrayList.stream().limit(2);
show("limitStream", limitStream);5. 丢弃 skip(n) 丢弃前n个元素
Stream<String> skipStream = arrayList.stream().skip(2);
show("skipStream", skipStream);6. 连接 Stream.concat() 将两个流连接起来,第一个流不能是无限流，否则第二个流没有处理的机会
Stream<String> concatStream = Stream.concat(arrayList.stream(), Stream.of("aa","bb","cc"));
show("concatStream", concatStream);7. 去重 distinct() 剔除重复元素
Stream<String> distinctStream = Stream.of("aa","bb","cc","aa").distinct();
show("distinctStream", distinctStream);8. 排序 sorted() 按照默认排序或者传入比较器
//(1) 按照默认排序, 字典顺序比较
Stream<String> sortedStream = Stream.of("aa","bb","cc","aa").sorted();
show("sortedStream", sortedStream);
sortedStream = Stream.of("aa","b1b","c22c","a33a","a4444b","a55555B").sorted(Comparator.comparing(x->x)); //提取Comparator进行排序
show("sortedStream", sortedStream);
//(2) 传入String的比较器
//1) 字典顺序比较
sortedStream = Stream.of("aa","bb","cc","aa","ab","aB").sorted(String::compareTo);
show("sortedStream", sortedStream);
sortedStream = Stream.of("aa","bb","cc","aa","ab","aB").sorted((x,y)->x.compareTo(y));
show("sortedStream", sortedStream);
//2) 比较length
sortedStream = Stream.of("aa","b1b","c22c","a33a","a4444b","a55555B").sorted(Comparator.comparing(String::length)); //提取Comparator进行排序
show("sortedStream", sortedStream);
sortedStream = Stream.of("aa","b1b","c22c","a33a","a4444b","a55555B").sorted((x,y)->Integer.compare(x.length(), y.length()));
show("sortedStream", sortedStream);
//3) 传入比较器 比较多个条件
sortedStream = Stream.of("aa","bb","cc","aa","ab","aB").sorted(
(x, y)->{
if(x.length()>y.length()){
return 1;
}else if(x.length()==y.length()){
return x.compareTo(y); //字典顺序比较
}else{
return -1;
}
});
show("sortedStream", sortedStream);
sortedStream = Stream.of("aa","bb","cc","aa","ab","aB").sorted(new Comparator<String>() {
@Override
public int compare(String x, String y) {
if(x.length()>y.length()){
return 1;
}else if(x.length()==y.length()){
return x.compareTo(y);
}else{
return -1;
}
}
});
show("sortedStream", sortedStream);
//4) 传入自定义的比较器 比较多个条件
sortedStream = Stream.of("aa","bb","cc","aa","ab","aB").sorted(ConvertStreamTest::myCompare);
show("sortedStream", sortedStream);
//5) 语法糖 比较多个条件
sortedStream = Stream.of("aa","b1b","c22c","a33a","a4444b","a55555B").sorted(Comparator.comparing(String::length).thenComparing(String::compareTo));
show("sortedStream", sortedStream);
//(3) reversed() 指定比较器倒叙
sortedStream = Stream.of("aa","b1b","c22c","a33a","a4444b","a55555B").sorted(Comparator.comparing((String x)->x).reversed());
show("sortedStream", sortedStream);
sortedStream = Stream.of("aa","b1b","c22c","a33a","a4444b","a55555B").sorted(Comparator.comparing(String::length).reversed());
show("sortedStream", sortedStream);9. 类似代理 peek() 获得每个元素时，做一些事情
Stream<String> peekStream = Stream.of("aa","b1b","c22c","a33a","a4444b","a55555B").peek(x->System.out.println("peek() fetch element： "+x));
show("peekStream", peekStream);最新文章
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