/**
* Constructs a new, empty tree map, using the natural ordering of its
* keys. All keys inserted into the map must implement the {@link
* Comparable} interface. Furthermore, all such keys must be
* <i>mutually comparable</i>: <tt>k1.compareTo(k2)</tt> must not throw
* a <tt>ClassCastException</tt> for any keys <tt>k1</tt> and
* <tt>k2</tt> in the map. If the user attempts to put a key into the
* map that violates this constraint (for example, the user attempts to
* put a string key into a map whose keys are integers), the
* <tt>put(Object key, Object value)</tt> call will throw a
* <tt>ClassCastException</tt>.
*/
public TreeMap() {
comparator = null;
}
/**
* Associates the specified value with the specified key in this map.
* If the map previously contained a mapping for the key, the old
* value is replaced.
*
* @param key key with which the specified value is to be associated
* @param value value to be associated with the specified key
*
* @return the previous value associated with <tt>key</tt>, or
* <tt>null</tt> if there was no mapping for <tt>key</tt>.
* (A <tt>null</tt> return can also indicate that the map
* previously associated <tt>null</tt> with <tt>key</tt>.)
* @throws ClassCastException if the specified key cannot be compared
* with the keys currently in the map
* @throws NullPointerException if the specified key is null
* and this map uses natural ordering, or its comparator
* does not permit null keys
*/
public V put(K key, V value) {
Entry<K,V> t = root;
if (t == null) {
// TBD:
// 5045147: (coll) Adding null to an empty TreeSet should
// throw NullPointerException
//
// compare(key, key); // type check
root = new Entry<K,V>(key, value, null);
size = 1;
modCount++;
return null;
}
int cmp;
Entry<K,V> parent;
// split comparator and comparable paths
Comparator<? super K> cpr = comparator;
if (cpr != null) {
do {
parent = t;
cmp = cpr.compare(key, t.key);
if (cmp < 0)
t = t.left;
else if (cmp > 0)
t = t.right;
else
return t.setValue(value);
} while (t != null);
}
else {
if (key == null)
throw new NullPointerException();
Comparable<? super K> k = (Comparable<? super K>) key;
do {
parent = t;
cmp = k.compareTo(t.key);
if (cmp < 0)
t = t.left;
else if (cmp > 0)
t = t.right;
else
return t.setValue(value);
} while (t != null);
}
Entry<K,V> e = new Entry<K,V>(key, value, parent);
if (cmp < 0)
parent.left = e;
else
parent.right = e;
fixAfterInsertion(e);
size++;
modCount++;
return null;
}
一个报错的场景：
package map; import java.util.Map;
import java.util.TreeMap; public class TreeMapDemo {
public static void main(String[] args) {
Map<Long, Staff> treeMap = new TreeMap<Long, Staff>();
for (int i = 0; i < 10; i++) {
treeMap.put(i + Math.round(Math.random() * 10), new Staff(i));
}
System.out.println(treeMap);
System.out.println("result:" + treeMap.containsKey(10));
System.out.println("result:" + treeMap.containsKey(1l)); }
} class Staff {
private int yearOfWorking; public Staff(int yearOfWorking) {
this.yearOfWorking = yearOfWorking;
} @Override
public String toString() {
return "Staff{" +
"yearOfWorking=" + yearOfWorking +
'}';
}
}
{5=Staff{yearOfWorking=1}, 7=Staff{yearOfWorking=5}, 9=Staff{yearOfWorking=7}, 10=Staff{yearOfWorking=9}, 11=Staff{yearOfWorking=2}, 13=Staff{yearOfWorking=8}}
Exception in thread "main" java.lang.ClassCastException: java.lang.Long cannot be cast to java.lang.Integer
at java.lang.Integer.compareTo(Integer.java:35)
at java.util.TreeMap.getEntry(TreeMap.java:328)
at java.util.TreeMap.containsKey(TreeMap.java:209)
at map.TreeMapDemo.main(TreeMapDemo.java:13)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:597)
at com.intellij.rt.execution.application.AppMain.main(AppMain.java:140)