TreeMap cannot be cast to java.lang.Comparable

 

 

    /**
     * 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)