/**     * 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     * mutually comparable: k1.compareTo(k2) must not throw     * a ClassCastException for any keys k1 and     * k2 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     * put(Object key, Object value) call will throw a     * ClassCastException.     */    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 key, or     *         null if there was no mapping for key.     *         (A null return can also indicate that the map     *         previously associated null with key.)     * @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
     
       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
      
       (key, value, null);            size = 1;            modCount++;            return null;        }        int cmp;        Entry
       
         parent;        // split comparator and comparable paths        Comparator
         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
         k = (Comparable
        ) 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
        
          e = new Entry
         
          (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
     
       treeMap = new TreeMap
      
       ();        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)