update:demo6

com/study/demo6/SumThread.java

@@ -0,0 +1,52 @@
+package com.study.demo6;
+
+public class SumThread {
+  static class PartSumTask implements Runnable {
+    private final int[] array;
+    private final int start;
+    private final int end;
+    public long result;
+
+    public PartSumTask(int[] array, int start, int end) {
+      this.array = array;
+      this.start = start;
+      this.end = end;
+    }
+
+    @Override
+    public void run() {
+      long sum = 0;
+      for (int i = start; i <= end; i++) {
+        sum += array[i];
+      }
+      result = sum;
+    }
+  }
+
+  public static void main(String[] args) throws InterruptedException {
+    int size = 1_000_000;
+    int[] array = new int[size];
+    for (int i = 0; i < size; i++) {
+      array[i] = i;
+    }
+
+    PartSumTask task1 = new PartSumTask(array, 0, 333_333);
+    PartSumTask task2 = new PartSumTask(array, 333_334, 666_666);
+    PartSumTask task3 = new PartSumTask(array, 666_667, 999_999);
+
+    Thread t1 = new Thread(task1);
+    Thread t2 = new Thread(task2);
+    Thread t3 = new Thread(task3);
+
+    t1.start();
+    t2.start();
+    t3.start();
+
+    t1.join();
+    t2.join();
+    t3.join();
+
+    long total = task1.result + task2.result + task3.result;
+    System.out.println("总和为：" + total);
+  }
+}