多个线程对hashmap进行put操作的异常

多个线程对hashmap进行put操作的异常

Exception in thread "Thread-0" java.lang.ClassCastException: java.util.HashMap$Node cannot be cast to java.util.HashMap$TreeNode
	at java.util.HashMap$TreeNode.moveRootToFront(HashMap.java:1832)
	at java.util.HashMap$TreeNode.treeify(HashMap.java:1949)
	at java.util.HashMap$TreeNode.split(HashMap.java:2175)
	at java.util.HashMap.resize(HashMap.java:714)
	at java.util.HashMap.putVal(HashMap.java:663)
	at java.util.HashMap.put(HashMap.java:612)
	at com.stono.thread3.page313.Thread1A.run(Thread1A.java:17)

源码：

package com.stono.thread3.page313;

import java.util.HashMap;

public class MyService1 {
    public HashMap<String, String> map = new HashMap<>();
}
package com.stono.thread3.page313;

import com.stono.thread3.CusPrint;

public class Thread1A extends Thread {

    private MyService1 service1;

    public Thread1A(MyService1 service1) {
        super();
        this.service1 = service1;
    }
    
    @Override
    public void run() {
        for(int i=0;i<50000;i++) {
            service1.map.put("ThreadA"+(i+1), "ThreadA"+(i+1));
            CusPrint.print("ThreadA"+(i+1));
        }
    }
}
package com.stono.thread3.page313;

import com.stono.thread3.CusPrint;

public class Thread1B extends Thread {

    private MyService1 service1;

    public Thread1B(MyService1 service1) {
        super();
        this.service1 = service1;
    }
    
    @Override
    public void run() {
        for(int i=0;i<50000;i++) {
            service1.map.put("ThreadB"+(i+1), "ThreadB"+(i+1));
            CusPrint.print("ThreadB"+(i+1));
        }
    }
}
package com.stono.thread3.page313;

public class Test1_2 {

    public static void main(String[] args) {
        MyService1 service1 = new MyService1();
        Thread1A a = new Thread1A(service1);
        Thread1B b = new Thread1B(service1);
        a.start();
        b.start();
    }

}