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TreeSet和TreeMap的输出
如果加入TreeSet和TreeMap的元素没有实现comprable中的compareTo()方法,那么会报错“treeset cannot be cast to java.lang.Comparable”.
因此需要对元素类型实现comparable借口,并实现compareTo()方法,即告诉TreeSet和TreeMap你要怎么排列,它才能进行排序。
基础类:
package niukewang; import java.util.Objects; public class setClass implements Comparable<setClass>{ String a; String b; public setClass(String a, String b) { this.a=a; this.b=b; } public int hashCode() { return a.hashCode(); } public boolean equals(Object obj) { if(obj==null) return false; if(getClass() != obj.getClass()) return false; final setClass s=(setClass)obj; return Objects.equals(this.a, s.a); } @Override public int compareTo(setClass o) { int num=this.b.compareTo(o.b); return num; } }
测试类:
package niukewang; import java.util.ArrayList; import java.util.HashMap; import java.util.HashSet; import java.util.Hashtable; import java.util.Iterator; import java.util.LinkedList; import java.util.List; import java.util.Map; import java.util.Set; import java.util.TreeMap; import java.util.TreeSet; import java.util.Vector; public class test1 { public static void main(String args[]) { setClass s1=new setClass("http://www.yjbys.com/", "same0"); setClass s2=new setClass("http://www.yjbys.com1/", "same0"); setClass s3=new setClass("http://www.yjbys.com2/", "same2"); setClass s4=new setClass("http://www.yjbys.com2/", "same3"); //hasSet System.out.println("hasSet......"); Set<setClass> set=new HashSet<setClass>(); set.add(s1); set.add(s2); set.add(s3); set.add(s4); Iterator it= set.iterator(); while(it.hasNext()) { setClass ob=(setClass)it.next(); System.out.println(ob.a); } //TreeSet System.out.println("\nTreeSet........"); Set<setClass> tree=new TreeSet<setClass>(); tree.add(s1); tree.add(s2); tree.add(s3); tree.add(s4); Iterator treeit=tree.iterator(); while(treeit.hasNext()) { setClass ob=(setClass) treeit.next(); System.out.println(ob.a); } //TreeMap System.out.println("\nTreeMap........."); Map<setClass,String> treemap=new TreeMap<setClass,String>(); treemap.put(s1, "TreeMap one"); treemap.put(s2, "TreeMap two"); treemap.put(s3, "TreeMap three"); treemap.put(s4, "TreeMap four"); for(Map.Entry<setClass, String> entry: treemap.entrySet()) { System.out.println("The treemap key is "+entry.getKey().a+" The value is "+ entry.getValue()); } //HasMap System.out.println("\nHashMap......"); Map<setClass,String> hashmap=new HashMap<setClass, String>(); hashmap.put(s1, "HashMap one"); hashmap.put(s2, "HashMap two"); hashmap.put(s3, "HashMap three"); hashmap.put(s4, "HashMap four"); for(Map.Entry<setClass, String> entry : hashmap.entrySet()) { System.out.println("The key is "+entry.getKey().a+" The value is "+entry.getValue()); } //HasTable System.out.println("\nHashTable......"); Map<setClass,String> hashtable=new Hashtable<setClass, String>(); hashtable.put(s1, "HashTable one"); hashtable.put(s2, "HashTable two"); hashtable.put(s3, "HashTable three"); hashtable.put(s4, "HashTable four"); for(Map.Entry<setClass, String> entry: hashtable.entrySet()) { System.out.println("The HashTable key is "+entry.getKey().a+" The HashTable value is "+entry.getValue()); } //LinkedList System.out.println("\nLinkedList....."); List list=new LinkedList(); list.add(s1); list.add(s2); list.add(s3); list.add(s4); Iterator listit=list.iterator(); while(listit.hasNext()) { setClass ob=(setClass)listit.next(); System.out.println(ob.a); } //ArrayList System.out.println("\nArrayList....."); List array=new ArrayList(); array.add(s1); array.add(s2); array.add(s3); array.add(s4); Iterator arrayit=array.iterator(); while(arrayit.hasNext()) { setClass ob=(setClass)arrayit.next(); System.out.println(ob.a); } //vector System.out.println("\nvector....."); Vector v=new Vector(); v.add(s1); v.add(s2); v.add(s3); v.add(s4); Iterator vit=v.iterator(); while(vit.hasNext()) { setClass ob=(setClass)vit.next(); System.out.println(ob.a); } } }
输出结果:
hasSet...... http://www.yjbys.com1/ http://www.yjbys.com/ http://www.yjbys.com2/ TreeSet........ http://www.yjbys.com/ http://www.yjbys.com2/ http://www.yjbys.com2/ TreeMap......... The treemap key is http://www.yjbys.com/ The value is TreeMap two The treemap key is http://www.yjbys.com2/ The value is TreeMap three The treemap key is http://www.yjbys.com2/ The value is TreeMap four HashMap...... The key is http://www.yjbys.com1/ The value is HashMap two The key is http://www.yjbys.com/ The value is HashMap one The key is http://www.yjbys.com2/ The value is HashMap four HashTable...... The HashTable key is http://www.yjbys.com1/ The HashTable value is HashTable two The HashTable key is http://www.yjbys.com/ The HashTable value is HashTable one The HashTable key is http://www.yjbys.com2/ The HashTable value is HashTable four LinkedList..... http://www.yjbys.com/ http://www.yjbys.com1/ http://www.yjbys.com2/ http://www.yjbys.com2/ ArrayList..... http://www.yjbys.com/ http://www.yjbys.com1/ http://www.yjbys.com2/ http://www.yjbys.com2/ vector..... http://www.yjbys.com/ http://www.yjbys.com1/ http://www.yjbys.com2/ http://www.yjbys.com2/
TreeSet并不像hashSet那样,用hashCode和equals取决于元素是否相等。
而是取决于compareTo()方法中指定的排序的方式;
setClass s1=new setClass("http://www.yjbys.com/", "same0");
setClass s2=new setClass("http://www.yjbys.com1/", "same0");
setClass s3=new setClass("http://www.yjbys.com2/", "same2");
setClass s4=new setClass("http://www.yjbys.com2/", "same3");
如果用hashCode和equals取决于元素是否相等,那么s3和s4是相等的;
而此时候,是根据compareTo()方法中的第二个字符串b来判断是否相等,则s1与s2相等,s3和s4不相等,所以才有这样的输出:
TreeSet........
http://www.yjbys.com/
http://www.yjbys.com2/
http://www.yjbys.com2/
TreeSet和TreeMap的输出