public class TreeMapTest {
public static void main(String[] args) {
Map<Student,Integer> students = new TreeMap<>();
students.put(new Student("11"),1);
students.put(new Student("11"),1);
System.out.println(students.size());
}
}输出结果为2
因为
public V put(K key, V value) {
Entry<K,V> t = root;
if (t == null) {
compare(key, key); // type (and possibly null) check
root = new Entry<>(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();
@SuppressWarnings("unchecked")
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<>(key, value, parent);
if (cmp < 0)
parent.left = e;
else
parent.right = e;
fixAfterInsertion(e);
size++;
modCount++;
return null;
}上面红色字体：调用compareTo方法，看结果来看新存入的值放在左侧（cmp<0），还是右侧(cmp>0)，还是现在的value值把原来的value值覆盖(cmp=0)
需要在Student类中重写compareTo方法
@Override
public int compareTo(Student o) {
return 0;
}
按照你自己的要求重写compareTo方法就行了~