java 如何比较java中的两个哈希集？
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How to compare two hash sets in java?
提问by user8048032
How can I compare two hash sets in java ? My first hash sets looks like below.
如何比较 java 中的两个哈希集？我的第一个哈希集如下所示。
static Set<String> nounPhrases = new HashSet<>();
Above hash set contains elements like this.
上面的哈希集包含这样的元素。
List of Noun Parse : [java, jsp, book]
名词解析列表：[java, jsp, book]
2nd hash set
第二个哈希集
static Set<String> nounPhrases2 = new HashSet<>();
List of Noun Parse : [web, php, java,book]
名词解析列表：[web, php, java,book]
Note - I need to check if there are equal nouns in both sets. and if they have similar nouns then I need to do another task
注意 - 我需要检查两组中是否有相同的名词。如果他们有相似的名词，那么我需要做另一项任务
回答by Bohemian
This is a wheel already invented.
这是一个已经发明的轮子。
Set#equals()compares sets in the way you would expect:
Set#equals()以您期望的方式比较集合：
set1.equals(set2)
If you want two Set variables that are both null to be "equal", then use:
如果您希望两个都为 null 的 Set 变量“相等”，请使用：
Objects.equals(set1, set2)
回答by Dennux
So you mean like this?
所以你的意思是这样？
public static void main(String[] args) {
final Set<String> nounPhrases = new HashSet<>();
nounPhrases.add("java");
nounPhrases.add("jsp");
nounPhrases.add("book");
final Set<String> nounPhrases2 = new HashSet<>();
nounPhrases2.add("web");
nounPhrases2.add("php");
nounPhrases2.add("java");
nounPhrases2.add("book");
// Checking for every element in first set
for (final String element : nounPhrases) {
// if second set has the current element
if (nounPhrases2.contains(element)) {
System.out.println("They have " + element);
}
}
}
My output:
我的输出：
They have java
They have book
Edit: Based on your comment, if i understand correctly, if you want to get the common elements in both sets, just store the values and return them:
编辑：根据您的评论，如果我理解正确，如果您想获取两个集合中的公共元素，只需存储值并返回它们：
public static void main(String[] args) {
final Set<String> nounPhrases = new HashSet<>();
nounPhrases.add("java");
nounPhrases.add("jsp");
nounPhrases.add("book");
final Set<String> nounPhrases2 = new HashSet<>();
nounPhrases2.add("web");
nounPhrases2.add("php");
nounPhrases2.add("java");
nounPhrases2.add("book");
System.out.println(getCommon(nounPhrases, nounPhrases2));
}
public final static Set<String> getCommon(Set<String> setA, Set<String> setB) {
final Set<String> result = new HashSet<>();
for (final String element : setA) {
if (setB.contains(element)) {
result.add(element);
}
}
return result;
}
You could use generics to make the method work for other elements than strings:
您可以使用泛型使该方法适用于字符串以外的其他元素：
public final static <T> Set<T> getCommon(Set<T> setA, Set<T> setB) {
final Set<T> result = new HashSet<>();
for (final T element : setA) {
if (setB.contains(element)) {
result.add(element);
}
}
return result;
}
If performance is important, you should check sizes first and only iterate over the elements of the smaller set. If you have one set with 1 elements, and one set with 100, starting with the smaller will leve you with one iteration whereas starting with the bigger will leave you with 100 checks where only 1 could have been in both sets.
如果性能很重要，您应该首先检查大小，并且只迭代较小集合的元素。如果你有一个有 1 个元素的集合，一个有 100 个元素的集合，从较小的开始会让你进行一次迭代，而从较大的开始会给你留下 100 个检查，而这两个集合中只有 1 个。
回答by UchihaObito
If u want to find the common element then use collect(Collectors.toList()) instead of count , If u want simply to find how many set has common element using java 8
如果您想找到公共元素，则使用 collect(Collectors.toList()) 而不是 count ，如果您只想使用 java 8 查找有多少集合具有公共元素
long count = nounPhrases.stream().filter(tempstring -> {
return nounPhrases2.stream().anyMatch(tempstring2 -> {
return tempstring.equals(tempstring2);
});
}).count();
if (count > 0)
System.out.println("has common elements-"+count);
else
System.out.println("not common");
回答by Mayur Ingle
By the use of Java apache.commons.collections package we can implement
通过使用Java apache.commons.collections包我们可以实现
package com.StackoverFlow;
import java.util.Collection;
import java.util.HashSet;
import java.util.Set;
import org.apache.commons.collections.CollectionUtils;
public class MainClass {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Set hs_1 = new HashSet();
hs_1.add("A");
hs_1.add("B");
hs_1.add("C");
hs_1.add("D");
Set hs_2 = new HashSet();
hs_2.add("A");
hs_2.add("B");
hs_2.add("C");
hs_2.add("D");
Collection result = CollectionUtils.subtract(hs_1, hs_2);
System.out.println(result);
if(result.isEmpty()){
System.out.println("perform Task-->>Value maches ");
}else{
System.out.println("perform Task-->>Value not maches ");
}
}
}
回答by Binu
public class SetUtils {
public static boolean equals(Set<?> set1, Set<?> set2){
if(set1 == null || set2 ==null){
return false;
}
if(set1.size()!=set2.size()){
return false;
}
return set1.containsAll(set2);
}
}
