統計List中的元素重複出現的次數
阿新 • • 發佈:2019-01-06
import java.util.ArrayList;import java.util.Collections;import java.util.HashMap;import java.util.HashSet;import java.util.List;import java.util.Map;import java.util.Set;import java.util.TreeMap;public class CountDuplicatedList {public static void main(String[] args) {List list = new ArrayList(); list.add("a"); list.add("b"); list.add("c"); list.add("d"); list.add("b"); list.add("c"); list.add("a"); list.add("a"); list.add("a"); System.out.println("\n例子 1 -統計'a'出現的頻率"); System.out.println("a : " + Collections.frequency(list, "a")); System.out.println("\n例子 2 - 統計每一個元素出現的頻率"); //將List轉換為Set Set uniqueSet = new HashSet(list); for (String temp : uniqueSet) { System.out.println(temp + ": " + Collections.frequency(list, temp)); } System.out.println("\n例子 3 - 用Map統計每個元素出現的頻率"); Map map = new HashMap(); for (String temp : list) { Integer count = map.get(temp); map.put(temp, (count == null) ? 1 : count + 1); } printMap(map); System.out.println("\nSorted Map"); Map treeMap = new TreeMap(map); printMap(treeMap); } public static void printMap(Map map){ for (Map.Entry entry : map.entrySet()) { System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue()); } } }
list.add("a");
list.add("b");
list.add("c");
list.add("d");
list.add("b");
list.add("c");
list.add("a");
list.add("a");
list.add("a");
System.out.println("\n例子 1 -統計'a'出現的頻率");
System.out.println("a : " + Collections.frequency(list, "a"));
System.out.println("\n例子 2 - 統計每一個元素出現的頻率");
//將List轉換為Set
Set uniqueSet = new HashSet(list); for (String temp : uniqueSet) { System.out.println(temp + ": " + Collections.frequency(list, temp)); } System.out.println("\n例子 3 - 用Map統計每個元素出現的頻率"); Map map = new HashMap(); for (String temp : list) { Integer count = map.get(temp); map.put(temp, (count == null) ? 1 : count + 1); } printMap(map); System.out.println("\nSorted Map"); Map treeMap = new TreeMap(map); printMap(treeMap); } public static void printMap(Map map){ for (Map.Entry entry : map.entrySet()) { System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue()); } } }
for (String temp : uniqueSet) {
System.out.println(temp + ": " + Collections.frequency(list, temp));
}
System.out.println("\n例子 3 - 用Map統計每個元素出現的頻率");
Map map = new HashMap(); for (String temp : list) { Integer count = map.get(temp); map.put(temp, (count == null) ? 1 : count + 1); } printMap(map); System.out.println("\nSorted Map"); Map treeMap = new TreeMap(map); printMap(treeMap); } public static void printMap(Map map){ for (Map.Entry entry : map.entrySet()) { System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue()); } } }
for (String temp : list) {
Integer count = map.get(temp);
map.put(temp, (count == null) ? 1 : count + 1);
}
printMap(map);
System.out.println("\nSorted Map");
Map treeMap = new TreeMap(map); printMap(treeMap); } public static void printMap(Map map){ for (Map.Entry entry : map.entrySet()) { System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue()); } } }
printMap(treeMap);
}
public static void printMap(Map map){ for (Map.Entry entry : map.entrySet()) { System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue()); } } }
for (Map.Entry entry : map.entrySet()) { System.out.println("Key : " + entry.getKey() + " Value : " + entry.getValue()); } } }
System.out.println("Key : " + entry.getKey() + " Value : "
+ entry.getValue());
}
}
}
結果:
例子 1 -統計'a'出現的頻率a : 4例子 2 - 統計每一個元素出現的頻率d: 1b: 2c: 2a: 4例子 3 - 用Map統計每個元素出現的頻率Key : d Value : 1Key : b Value : 2Key : c Value : 2Key : a Value : 4Sorted MapKey : a Value : 4Key : b Value : 2Key : c Value : 2Key : d Value : 1