40 lines
1.3 KiB
Java
40 lines
1.3 KiB
Java
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package jTest;
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import java.util.Arrays;
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import java.util.HashMap;
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import java.util.List;
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import java.util.Map;
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import java.util.stream.IntStream;
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public class StreamTest {
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public static void main(String[] args) {
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// 创建二维数组
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List<List<String>> list1 = Arrays.asList(
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Arrays.asList("a", "b", "c"),
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Arrays.asList("a", "b", "c")
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);
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// 二维数组平整化
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List<String> list = list1.stream().flatMap(List::stream).toList();
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System.out.println(list);// [a, b, c, a, b, c]
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// peek可以用来调试也可以塞对象，不改变流，如果你这个里面有对象，比如xxx.setXXX() 那么也会修改这个对象
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List<String> list2 = list.stream().filter(s -> s.startsWith("a"))
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.peek(System.out::println)
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.map(String::toUpperCase).toList();
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System.out.println(list2);// [A, A]
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// 求和
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int sum = IntStream.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).sum();
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System.out.println(sum);
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// Map集合
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Map<String, Integer> counts = new HashMap<>();
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counts.put("apple", 1);
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counts.put("banana", 1);
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System.out.println(counts);
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counts.compute("apple", (key, val) -> val == null ? 1 : val + 1);
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System.out.println(counts);
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}
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}
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