在Java中合并两个集合

set 接口存在于Java.util 包中，并扩展了 Collection 接口，它是一个无序的对象集合，其中不能存储重复值。它是一个实现数学集的接口。该接口包含从 Collection 接口继承的方法，并添加了限制重复元素插入的功能。有两个扩展集合实现的接口，即 SortedSet 和 NavigableSet。

方法：以下是在Java中合并两个集合的各种方法：

1. 使用双括号初始化
2. 使用 Set 类的 addAll() 方法
   • 使用用户定义的方法
   • 在用户定义函数中使用Java 8 流
3. 在用户定义函数中使用Java 8 流
4. Stream类的of()和forEach()方法的使用
5. 使用 Collector 的 Stream 类的 of() 和 flatMap() 方法
6. 使用带有收集器的 Stream 类的 concat() 方法
7. 使用 Apache 公共集合
8. 使用 Guava Iterables.concat()
   

方法一：使用双大括号初始化

插图：

Input :  a = [1, 3, 5, 7, 9]
         b = [0, 2, 4, 6, 8]
Output : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例子

Java

// Java Program to Demonstrate Merging of two sets in Java
// Using Double brace Initialization
  
// Importing required classes
import java.io.*;
import java.util.*;
import java.util.stream.*;
  
// Main class
public class GFG {
  
    // Method 1
    // To merge two sets
    // using DoubleBrace Initialisation
    public static  Set mergeSet(Set a, Set b)
    {
  
        // Adding all elements of respective Sets
        // using addAll() method
        return new HashSet() {
            {
                addAll(a);
                addAll(b);
            }
        };
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
  
        // Creating the sets to be merged
  
        // First set
        Set a = new HashSet();
        // Applying Arrays.asList()
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second set
        Set b = new HashSet();
        // Applying Arrays.asList()
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing the Sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling Method 1 to merge above Sets
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

方法二：使用Set类的addAll()方法

addAll() 方法由 Set 接口提供。它将作为参数传递的元素添加到该集合的最后一个。

2-A。使用用户定义的方法

插图：

Input  : a = [1, 3, 5, 7, 9]
         b = [0, 2, 4, 6, 8]
Output : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例子：

Java

// Java program to demonstrate Merging of Two Sets
// Using SetAll() method
  
// Importing required classes
import java.util.*;
  
// Main class
public class GFG {
  
    // Method 1
    // To merge two sets
    // using addAll()
    public static  Set mergeSet(Set a, Set b)
    {
  
        // Creating an empty HashSet
        Set mergedSet = new HashSet();
  
        // Adding the two sets to be merged
        // into the new Set using addAll() method
        mergedSet.addAll(a);
        mergedSet.addAll(b);
  
        // Returning the merged set
        return mergedSet;
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
  
        // Creating the sets to be merged
  
        // First Set
        Set a = new HashSet();
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second Set
        Set b = new HashSet();
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing the Sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling method 1 to merge above Sets
        // and printing it
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

2-B。在用户定义函数中使用Java 8 流

插图：

Input : a = [1, 3, 5, 7, 9]
        b = [0, 2, 4, 6, 8]
Output : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例子

Java

// Java program to demonstrate Merging of Two Sets
// Using Stream
  
// Importing required classes
import java.io.*;
import java.util.*;
import java.util.stream.*;
  
// Main class
public class GFG {
  
    // Method 1
    // To merge two Sets
    // using addAll()
    public static  Set mergeSet(Set a, Set b)
    {
  
        // Creating a Set with 'a'
        Set mergedSet
            = a.stream().collect(Collectors.toSet());
  
        // Adding the second set to be merged
        mergedSet.addAll(b);
  
        // Returning the merged Set
        return mergedSet;
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
        // Creating the Sets to be merged
  
        // First set
        Set a = new HashSet();
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second set
        Set b = new HashSet();
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing above Sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling method 1 to merge two Sets
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

方法三：使用 Collections 类的 addAll() 方法

插图：

Input :   a = [1, 3, 5, 7, 9]
          b = [0, 2, 4, 6, 8]
Output :  [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例子：

Java

// Java Program to Merge Two Arrays
// of Same Type into an Object Array
  
// Importing required classes
import java.io.*;
import java.util.*;
  
// Main class
class GFG {
  
    // Method 1
    // To merging two Sets
    // using addAll()
    public static Set mergeSet(Set a,
                                        Set b)
    {
  
        // Creating an empty HashSet of Integer type
        Set mergedSet = new HashSet<>();
  
        // Adding the two sets to be merged
        // into the new Set
        Collections.addAll(mergedSet,
                           a.toArray(new Integer[0]));
        Collections.addAll(mergedSet,
                           b.toArray(new Integer[0]));
  
        // Returning the merged Set
        return mergedSet;
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
  
        // Creating the sets to be merged
  
        // First set
        Set a = new HashSet();
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second set
        Set b = new HashSet();
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing the above two Sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling above method 1 to merge two sets
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

方法四：使用Stream类的of()和forEach()方法

插图：

Input : a = [1, 3, 5, 7, 9]
        b = [0, 2, 4, 6, 8]
Output : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例子：

Java

// Java Program to Demonstrate Merging of Two Sets
// Using Stream
  
// Importing required classes
import java.io.*;
import java.util.*;
import java.util.stream.*;
  
// Main class
public class GFG {
  
    // Method  1
    // To merge two sets
    // using Stream of() and forEach() methods
    public static  Set mergeSet(Set a, Set b)
    {
  
        // Creating an empty set
        Set mergedSet = new HashSet();
  
        // add the two sets to be merged
        // into the new set
        Stream.of(a, b).forEach(mergedSet::addAll);
  
        // returning the merged set
        return mergedSet;
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
  
        // Creating the sets to be merged
  
        // First set
        Set a = new HashSet();
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second set
        Set b = new HashSet();
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing the above two Sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling method 1 to merge two Sets
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

方法五：使用Stream类的of()和flatMap()方法和Collector

插图：

Input :  a = [1, 3, 5, 7, 9]
         b = [0, 2, 4, 6, 8]
Output : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例子：

Java

// Java Program to Demonstrate Merging of Two Sets
// Using stream
  
// Importing required classes
import java.io.*;
import java.util.*;
import java.util.stream.*;
  
// Main class
public class GFG {
  
    // Method 1
    // To merge two Sets
    // using Stream of(), flatMap() and Collector
    public static  Set mergeSet(Set a, Set b)
    {
  
        // Adding the two Sets to be merged
        // into the new Set and
        // returning the merged set
        return Stream.of(a, b)
            .flatMap(x -> x.stream())
            .collect(Collectors.toSet());
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
        // Creating the sets to be merged
  
        // First Set
        Set a = new HashSet();
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second Set
        Set b = new HashSet();
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing the sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling method 1 to merge above two Sets
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

方法六：使用Stream类的concat()方法和Collector

插图：

Input : a = [1, 3, 5, 7, 9]
        b = [0, 2, 4, 6, 8]
Output : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

concatenate函数用于合并到字符串并生成一个包含两个字符串的字符串。 Stream.concat() 方法创建一个惰性连接流，其元素是第一个流的所有元素，然后是第二个流的所有元素。

例子

Java

// Java program to Demonstrate Merging of two Sets
// using Stream
  
// Importing required classes
import java.io.*;
import java.util.*;
import java.util.stream.*;
  
// Main class
public class GFG {
  
    // Method 1
    // To merge two sets
    // using Stream concat() and Collectors
    public static  Set mergeSet(Set a, Set b)
    {
  
        // Adding the two sets to be merged
        // into the new Set and
        // returning the merged set
        return Stream.concat(a.stream(), b.stream())
            .collect(Collectors.toSet());
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
        // Creating the sets to be merged
  
        // First Set
        Set a = new HashSet();
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second Set
        Set b = new HashSet();
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing the above two Sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling the method 1 to merge two Sets
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

方法 7：使用 Apache Common Collections

插图：

Input :  a = [1, 3, 5, 7, 9]
         b = [0, 2, 4, 6, 8]
Output : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例子

Java

// Java Program to Demonstrate Merging of Two Sets
// Using Apache Common Collection
  
// Importing required classes
import java.io.*;
import java.util.*;
import org.apache.commons.collections4.SetUtils;
  
// Main class
public class GFG {
  
    // Method 1
    // To merge two Sets
    // using addAll() method
    public static  Set mergeSet(Set a, Set b)
    {
  
        // Adding the two Sets to be merged
        // into the new Set and
        // returning the merged Set
        return SetUtils.union(a, b);
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
  
        // Creating the Sets to be merged
  
        // First set
        Set a = new HashSet();
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second set
        Set b = new HashSet();
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing the above two Sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling method 1 to merge two Sets
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

方法 8：使用 Guava Iterables.concat()

插图：

Input : a = [1, 3, 5, 7, 9]
        b = [0, 2, 4, 6, 8]
Output : [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

例子

Java

// Java Program to Demonstrate Merging of Two Sets
// Using Guava Library
  
// Importing required classes
import com.google.common.collect.Iterables;
import com.google.common.collect.Sets;
import java.io.*;
import java.util.*;
  
// Main class
public class GFG {
  
    // Method 1
    // To merge two sets
    // using Guava Iterables.concat()
    public static  Set mergeSet(Set a, Set b)
    {
  
        // Adding the two sets to be merged
        // into the new set and
        // returning the merged set
        return Sets.newHashSet(Iterables.concat(a, b));
    }
  
    // Method 2
    // Main driver method
    public static void main(String[] args)
    {
  
        // Creating the Sets to be merged
  
        // First set
        Set a = new HashSet();
        a.addAll(
            Arrays.asList(new Integer[] { 1, 3, 5, 7, 9 }));
  
        // Second set
        Set b = new HashSet();
        b.addAll(
            Arrays.asList(new Integer[] { 0, 2, 4, 6, 8 }));
  
        // Printing the above two Sets
        System.out.println("Set a: " + a);
        System.out.println("Set b: " + b);
  
        // Calling method 1 to merge two Sets
        System.out.println("Merged Set: " + mergeSet(a, b));
    }
}

输出：

Set a: [1, 3, 5, 7, 9]
Set b: [0, 2, 4, 6, 8]
Merged Set: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9]

Note: Any duplicate element presented in the sets will be discarded during the merge in all the above methods.