被for循环坑了

时间 2019-11-06

标签循环繁體版

原文原文链接

测试代码以下app

@Test
    public void test_2(){
        List<AuthorizeContractBean> list = new ArrayList<>();
        AuthorizeContractBean b = new AuthorizeContractBean();
        for (int i = 0; i < 1000; i++) {
            b.setBorrowerId(String.valueOf(i));
            if(i % 2 == 0){
                b.setPlatformNo("aaaa");
                b.setFileUrl("aaa-url");
            } else {
                b.setPlatformNo("bbbb");
                b.setFileUrl("bbb-url");
            }
            list.add(b);
            //logger.info(b.toString());
        }
        for (int i = 0; i < list.size(); i++) {
            logger.info(list.toString());
        }
    }

输出日志以下测试

16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.420 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.421 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.421 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.421 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.421 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.421 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}
16:07:59.421 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}

惊呆，list里装的id都变成了999，也就是都变成了最后一个add进list的对象。url

当时在封装一个带list对象的bean对象，发送给接口，再处理返回结果。返回结果发现几十个id都同样，郁闷了，觉得把for循环里的i写成1了，仔细排查代码才发现。日志

总之，不要在for循环里改变在for循环外建立的对象，这样会出现意想不到的后果！code

修改后代码以下：orm

@Test
    public void test_2(){
        List<AuthorizeContractBean> list = new ArrayList<>();
        for (int i = 0; i < 1000; i++) {
            // 把对象的建立放进for循环里
            AuthorizeContractBean b = new AuthorizeContractBean();
            b.setBorrowerId(String.valueOf(i));
            if(i % 2 == 0){
                b.setPlatformNo("aaaa");
                b.setFileUrl("aaa-url");
            } else {
                b.setPlatformNo("bbbb");
                b.setFileUrl("bbb-url");
            }
            list.add(b);
            //logger.info(b.toString());
        }
        for (int i = 0; i < list.size(); i++) {
            logger.info(list.get(i).toString());
        }
    }

此时运行测试类，输出结果以下：对象

16:11:49.029 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='0', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='1', fileUrl='bbb-url', platformNo='bbbb'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='2', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='3', fileUrl='bbb-url', platformNo='bbbb'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='4', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='5', fileUrl='bbb-url', platformNo='bbbb'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='6', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='7', fileUrl='bbb-url', platformNo='bbbb'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='8', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='9', fileUrl='bbb-url', platformNo='bbbb'}
16:11:49.031 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='10', 
fileUrl='aaa-url', platformNo='aaaa'}

······
16:11:49.073 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='992', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.073 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='993', fileUrl='bbb-url', platformNo='bbbb'}
16:11:49.073 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='994', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.073 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='995', fileUrl='bbb-url', platformNo='bbbb'}
16:11:49.073 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='996', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.073 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='997', fileUrl='bbb-url', platformNo='bbbb'}
16:11:49.073 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='998', fileUrl='aaa-url', platformNo='aaaa'}
16:11:49.073 [main] INFO  c.i.ups.app.contract.Test.ThreadTest - AuthorizeContractBean{borrowerId='999', fileUrl='bbb-url', platformNo='bbbb'}

这样就能够了！输出id为i的值从0到999接口