添加map、set、list操作

.gitignore

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+HELP.md
+target/
+!.mvn/wrapper/maven-wrapper.jar
+!**/src/main/**/target/
+!**/src/test/**/target/
+logs/
+### STS ###
+.apt_generated
+.classpath
+.factorypath
+.project
+.settings
+.springBeans
+.sts4-cache
+
+### IntelliJ IDEA ###
+.idea
+*.iws
+*.iml
+*.ipr
+
+### NetBeans ###
+/nbproject/private/
+/nbbuild/
+/dist/
+/nbdist/
+/.nb-gradle/
+build/
+!**/src/main/**/build/
+
+### VS Code ###
+.vscode/

jTest/StreamTest.java

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+package jTest;
+
+import java.util.Arrays;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import java.util.stream.IntStream;
+
+public class StreamTest {
+    public static void main(String[] args) {
+        // 创建二维数组
+        List<List<String>> list1 = Arrays.asList(
+                Arrays.asList("a", "b", "c"),
+                Arrays.asList("a", "b", "c")
+        );
+        // 二维数组平整化
+        List<String> list = list1.stream().flatMap(List::stream).toList();
+        System.out.println(list);// [a, b, c, a, b, c]
+
+        // 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
+        List<String> list2 = list.stream().filter(s -> s.startsWith("a"))
+                .peek(System.out::println)
+                .map(String::toUpperCase).toList();
+        System.out.println(list2);// [A, A]
+
+        // 求和
+        int sum = IntStream.of(1, 2, 3, 4, 5, 6, 7, 8, 9, 10).sum();
+        System.out.println(sum);
+
+        // Map集合
+        Map<String, Integer> counts = new HashMap<>();
+        counts.put("apple", 1);
+        counts.put("banana", 1);
+        System.out.println(counts);
+
+        counts.compute("apple", (key, val) -> val == null ? 1 : val + 1);
+        System.out.println(counts);
+    }
+}