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68
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1 package fschmidt.util.java;
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2
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3 import java.util.Collection;
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4 import java.util.Collections;
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5 import java.util.Map;
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6 import java.util.HashMap;
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7 import java.util.List;
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8 import java.util.ArrayList;
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9 import java.util.Set;
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10 import java.util.HashSet;
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11 import java.util.LinkedHashSet;
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12
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13
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14 public final class CollectionUtils {
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15 private CollectionUtils() {} // never
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16
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17 public static <K,V> Map<K,V> optimizeMap(Map<K,V> map) {
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18 switch( map.size() ) {
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19 case 0:
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20 return Collections.emptyMap();
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21 case 1:
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22 Map.Entry<K,V> entry = map.entrySet().iterator().next();
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23 return Collections.singletonMap(entry.getKey(),entry.getValue());
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24 default:
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25 return new HashMap<K,V>(map);
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26 }
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27 }
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28
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29 public static <T> List<T> optimizeList(List<T> list) {
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30 switch( list.size() ) {
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31 case 0:
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32 return Collections.emptyList();
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33 case 1:
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34 return Collections.singletonList(list.get(0));
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35 default:
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36 return new ArrayList<T>(list);
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37 }
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38 }
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39
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40 public static <T> Set<T> optimizeSet(Set<T> set) {
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41 switch( set.size() ) {
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42 case 0:
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43 return Collections.emptySet();
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44 case 1:
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45 return Collections.singleton(set.iterator().next());
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46 default:
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47 return new HashSet<T>(set);
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48 }
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49 }
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50
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51 public static <T> Set<T> optimizeLinkedSet(Set<T> set) {
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52 switch( set.size() ) {
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53 case 0:
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54 return Collections.emptySet();
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55 case 1:
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56 return Collections.singleton(set.iterator().next());
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57 default:
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58 return new LinkedHashSet<T>(set);
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59 }
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60 }
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61
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62 public static boolean intersects(Set set,Iterable col) {
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63 for( Object obj : col ) {
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64 if( set.contains(obj) )
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65 return true;
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66 }
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67 return false;
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68 }
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69
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70 public static boolean intersects(Set set,Object[] col) {
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71 for( Object obj : col ) {
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72 if( set.contains(obj) )
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73 return true;
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74 }
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75 return false;
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76 }
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77
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78 }
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