Question

我正在尝试修改从方法返回为Object集合的特定对象。现在还有很多其他对象也被添加到这个集合中。因此找到特定的对象变得困难。我尝试使用“instanceof”来解决它，但我得到以下异常：

java.lang.ClassCastException: com.sheesoft.MockBean cannot be cast to com.sheesoft.TestBean
at com.sheesoft.Main.main(Main.java:30)

我已经能够使用某些测试类重现相同的异常。请让我知道我哪里出错了。

主：

package com.sheesoft;

import java.util.ArrayList;
import java.util.Collection;
import java.util.Iterator;

public class Main {

/**
 * @param args
 */
public static void main(String[] args) {
    Collection<Object> beanCollection = new ArrayList<Object>();
    TestBean tb1 = new TestBean();
    MockBean mb1 = new MockBean();

    beanCollection.add(tb1);
    beanCollection.add(mb1);

    try{
    Iterator<Object> itr = beanCollection.iterator();
    while(itr.hasNext()){
        Object object = itr.next();
        if(object instanceof TestBean){
            TestBean tb2 = (TestBean) itr.next();
            tb2 = modifyTestBody(tb2);
            System.out.println(tb2.getBody());
        }
        if(object instanceof MockBean){
            MockBean mb2 = (MockBean) itr.next();
            System.out.println(mb2.getMockPayload());
        }
    }
    }catch(Exception e){
        e.printStackTrace();
    }
}

    private static TestBean modifyTestBody(TestBean tb) {
    tb.setBody("NewBody");
            return tb;
    }

}

Bean1：

package com.sheesoft;

public class TestBean {
private String header;
private String body;

public TestBean(){
    setHeader("header");
    setBody("body");
}

public String getHeader(){
    return header;
}
public String getBody(){
    return body;
}
public void setHeader(String header){
    this.header=header;
}
public void setBody(String body){
    this.body = body;
}
public String toString(){
    StringBuilder sb = new StringBuilder();
    sb.append("header = "+header+"\n");
    sb.append("body = "+body+"\n");
    String returns = sb.toString();
    return returns;
}
}

Bean 2：

package com.sheesoft;

public class MockBean {
private String mockHeader;
private String mockBody;
private String mockPayload; 

public MockBean(){
    setMockHeader("mockHeader");
    setMockBody("mockBody");
    setMockPayload("mockPayload");
}



public String getMockHeader(){
    return mockHeader;
}
public String getMockBody(){
    return mockBody;
}
public String getMockPayload(){
    return mockPayload;
}
public void setMockHeader(String header){
    this.mockHeader=header;
}
public void setMockBody(String body){
    this.mockBody = body;
}
public void setMockPayload(String payload) {
    this.mockPayload = payload;
}

public String toString(){
    StringBuilder sb = new StringBuilder();
    sb.append("mockHeader = "+mockHeader+"\n");
    sb.append("mockBody = "+mockBody+"\n");
    sb.append("mockPayload"+mockPayload+"\n");
    String returns = sb.toString();
    return returns;
}
}

Answer 1

在

    System.out.println(itr.next().toString());
    if(itr.next() instanceof TestBean){
        TestBean tb2 = (TestBean) itr.next();
                        tb2=modifyTestBody(tb2);
        System.out.println(tb2.getBody());
    }
    if(itr.next() instanceof MockBean){
        MockBean mb2 = (MockBean) itr.next();
        System.out.println(mb2.getMockPayload());
    }

您将分别致电itr.next()三次。当您只检查是否有一个元素可用时，会移动三个不同的元素。相反，将itr.next()存储到变量中并对该变量执行所有操作。

Answer 2

在您的代码中：

System.out.println(itr.next().toString());
        if(itr.next() instanceof TestBean){
            TestBean tb2 = (TestBean) itr.next();
                            tb2=modifyTestBody(tb2);
            System.out.println(tb2.getBody());

您已拨打itr.next()三次。所以当你写第三个itr.next()时你已经跳到了第三个元素。因此，在每个循环中，您将迭代为三个元素。因此，Iterator过早耗尽并抛出java.util.NoSuchElementException

修改请改用此代码：

while(itr.hasNext()){ Object obj = itr.next(); System.out.println(obj.toString()); if(obj instanceof TestBean){ TestBean tb2 = (TestBean) obj; tb2=modifyTestBody(tb2); System.out.println(tb2.getBody()); } if(obj instanceof MockBean){ MockBean mb2 = (MockBean) obj; System.out.println(mb2.getMockPayload()); } } }catch(Exception e){}

Answer 3

在您拥有的代码中

    System.out.println(itr.next().toString());
    if(itr.next() instanceof TestBean){
        TestBean tb2 = (TestBean) itr.next();
....

问题是，每次调用itr.next（）时，都会从集合中获取下一个对象，因此在这种情况下，您不需要一个对象，而是多个对象。

您应该将此代码更改为：

    Object object = itr.next();
    System.out.println(object.toString());
    if(object instanceof TestBean){
        TestBean tb2 = (TestBean) object;
....

从集合中获取对象

3 个答案: