Java 集合方法addAll，频率和不相交。

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import java.util.ArrayList;/*NowJava.com - 时代Java*/

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import java.util.List;

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import java.util.Arrays;

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import java.util.Collections;

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public class Main 

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{

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   public static void main(String[] args) 

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   {

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      // initialize list1 and list2

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      String[] colors = {"red", "white", "yellow", "blue"};

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      List<String> list1 = Arrays.asList(colors);

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      ArrayList<String> list2 = new ArrayList<>();

      /**

      时   代    Java - nowjava.com 提供 

      **/

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      list2.add("black"); // add "black" to the end of list2

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      list2.add("red"); // add "red" to the end of list2

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      list2.add("green"); // add "green" to the end of list2

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      list2.add("red"); // add "red" to the end of list2

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      list2.add("red"); // add "red" to the end of list2

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      System.out.print("Before addAll, list2 contains: ");

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      // display elements in vector

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      for (String s : list2)

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         System.out.printf("%s ", s);

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      Collections.addAll(list2, colors); // add colors Strings to list2

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      System.out.printf("%nAfter addAll, list2 contains: ");

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       for (String s : list2)

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         System.out.printf("%s ", s);

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       int frequency = Collections.frequency(list2, "red");

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      System.out.printf(                                   

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         "%nFrequency of red in list2: %d%n", frequency);  

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