Question

我有2个类，它们实现了名为IProcess的相同接口。

IProcess.java

    package org.XXX.module.workflow.bo.interfaces;

    public interface IProcess extends IMasterObject {

    INode getCurrentNode();
    INode getPreviousNode();
    long getLastChange();
    IWorkflow getWorkflow();
}

头等舱

package org.XXX.module.workflow.database.bo.impl;

import org.XXX.module.workflow.bo.interfaces.INode;
import org.XXX.module.workflow.bo.interfaces.IProcess;
import org.XXX.module.workflow.bo.interfaces.IWorkflow;
import org.XXX.module.workflow.database.jdbc.entity.ProcessEntity;

public class ProcessEntityWrapper implements IProcess {

private String id;
private INode currentNode;
private INode previousNode;
private long lastChange;
private IWorkflow workflow;

public ProcessEntityWrapper(ProcessEntity entity) {
    this.id = entity.getId();
    this.lastChange = entity.getLastChange();
}

@Override
public String getId() {
    return id;
}

@Override
public INode getCurrentNode() {
    return currentNode;
}

@Override
public INode getPreviousNode() {
    return previousNode;
}

@Override
public long getLastChange() {
    return lastChange;
}

@Override
public IWorkflow getWorkflow() {
    return workflow;
}

/**
 * @param currentNode the currentNode to set
 */
public void setCurrentNode(INode currentNode) {
    this.currentNode = currentNode;
}

/**
 * @param prevoiusNode the prevoiusNode to set
 */
public void setPreviousNode(INode previousNode) {
    this.previousNode = previousNode;
}

/**
 * @param workflow the workflow to set
 */
public void setWorkflow(IWorkflow workflow) {
    this.workflow = workflow;
}

}

第二课：

package org.XXX.module.workflow.bo.impl;

import org.XXX.module.workflow.bo.interfaces.INode;
import org.XXX.module.workflow.bo.interfaces.IProcess;
import org.XXX.module.workflow.bo.interfaces.IWorkflow;

public class Process implements IProcess {

public Process(String id, INode currentNode, INode previousNode,
        long lastChange, IWorkflow workflow) {
    this.id = id;
    this.currentNode = currentNode;
    this.previousNode = previousNode;
    this.lastChange = lastChange;
    this.workflow = workflow;
}

private String id;
private INode currentNode;
private INode previousNode;
private long lastChange;
private IWorkflow workflow;

@Override
public String getId() {
    return id;
}

@Override
public INode getCurrentNode() {
    return currentNode;
}

@Override
public INode getPreviousNode() {
    return previousNode;
}

@Override
public long getLastChange() {
    return lastChange;
}

@Override
public IWorkflow getWorkflow() {
    return workflow;
}

/**
 * @param currentNode the currentNode to set
 */
public void setCurrentNode(INode currentNode) {
    this.currentNode = currentNode;
}

/**
 * @param previousNode the previousNode to set
 */
public void setPreviousNode(INode previousNode) {
    this.previousNode = previousNode;
}

/**
 * @param lastChange the lastChange to set
 */
public void setLastChange(long lastChange) {
    this.lastChange = lastChange;
}

}

Part，抛出ClassCastException：

@Override
public void route(IProcess process, INode nextNode) {
    if(initializedClient == null) {
        return;
    }
    Process processImpl = (Process) process;
    processImpl.setPreviousNode(process.getCurrentNode());
    processImpl.setCurrentNode(nextNode);
    dataAccess.updateProcess(processImpl);
}

流程是ProcessEntityWrapper -Object， processImpl 是流程对象

我不知道，为什么特定代码会抛出 ClassCastException 。请问有人帮帮我吗？

由于

修改

@Override
public void updateProcess(IProcess process) {
    TypedQuery<ProcessEntity> q = em.createQuery(WorkflowAccessProperties.SELECT_PROCESSES_BY_ID,ProcessEntity.class);
    q.setParameter("id", process.getId());
    ProcessEntity entity = (ProcessEntity) q.getSingleResult();

    em.getTransaction().begin();
    entity.setLastChange(System.currentTimeMillis());

    String previousId = null;

    if(process.getPreviousNode() != null) {
        previousId = process.getPreviousNode().getId();
    }

    entity.setPreviousNodeId(previousId);
    entity.setCurrentNodeId(process.getCurrentNode().getId());
    em.getTransaction().commit();

}

Answer 1

虽然ProcessEntityWrapper和Process实现了相同的界面，但它们并没有相互扩展。

它们是实现相同接口的不同类。

任何类都可以实现接口。这并不意味着它们可以转换为彼此。

示例：牛和鸟可以实现相同的界面，但是你不能仅仅因为它们实现相同的界面而将牛转换为鸟。

public interface Speakable(){
   public String speak();
}

public class Cow implements Speakable(){
   public String speak(){
      return "moooo";
   }
}

public class Bird implements Speakable(){
   public String speak(){
      return "vik vik";
   }
}

2个类实现相同的接口 - ＆gt;抛出ClassCastException

1 个答案: