说，我有一个ArrayList：
List<Transaction> txList
我还有几个扩展基类的事务 - 事务：
public class ATransaction extends Transaction {...}
public class BTransaction extends Transaction {...}
public class CTransaction extends Transaction {...}
... 10-12 more different kind of Transactions extends Transaction class
在代码的某些部分，我将删除这些交易。
for (Object tx : transactions) {
if (tx instanceof ATransaction) {
CustomerSession.remove((ATransaction) t);
} else if (tx instanceof BTransaction) {
CustomerSession.remove((BTransaction) t);
} else if ...
}
CustomerSession:
public void remove(Transaction t) {
Iterator itr = txList.iterator();
while (itr.hasNext()) {
//How to compare the type of iterator with that of the argument "t" passed in the remove method and do an - iterator remove - below when the condition is met
itr.remove();
}
}
谢谢！
答案 0 :(得分：3)
如果你不知道这些类型，也许这个带有泛型的选项会更合适。 remove方法如下所示：
public void remove(Class<? extends Transaction> cls) {
Iterator itr = transactions.iterator();
while (itr.hasNext()) {
if (itr.next().getClass().equals(cls)) {
System.out.println("removing");
itr.remove();
}
}
}
签名Class<? extends Transaction> cls将确保您需要将类作为扩展Transaction的参数传递，并像ATransaction一样。
找到以下代码：
public class ListStuff {
List<Transaction> transactions = new ArrayList<>();
public ListStuff() {
//Add some data
transactions.add(new ATransaction());
transactions.add(new DTransaction());
transactions.add(new ATransaction());
transactions.add(new ATransaction());
transactions.add(new CTransaction());
transactions.add(new ATransaction());
transactions.add(new BTransaction());
transactions.add(new CTransaction());
transactions.add(new BTransaction());
transactions.add(new BTransaction());
transactions.add(new CTransaction());
transactions.add(new CTransaction());
transactions.add(new DTransaction());
remove(ATransaction.class); //This will remove all ATrasaction from the list
remove(BTransaction.class); // This will remove all BTransaction from the list
transactions.stream().forEach(System.out::println);
}
public void remove(Class<? extends Transaction> cls) {
Iterator itr = transactions.iterator();
while (itr.hasNext()) {
if (itr.next().getClass().equals(cls)) {
System.out.println("removing");
itr.remove();
}
}
}
public abstract class Transaction {
}
public class ATransaction extends Transaction{
@Override
public String toString() {
return "A";
}
}
public class BTransaction extends Transaction{
@Override
public String toString() {
return "B";
}
}
public class CTransaction extends Transaction{
@Override
public String toString() {
return "C";
}
}
public class DTransaction extends Transaction{
@Override
public String toString() {
return "D";
}
}
}
答案 1 :(得分：2)
您也可以使用迭代器：
fit$where[fit$where==3] # for Node 3
# Hornet 4 Drive Hornet Sportabout Valiant Duster 360 Merc 240D Merc 280 Merc 280C
# 3 3 3 3 3 3 3
# Merc 450SE Merc 450SL Merc 450SLC Cadillac Fleetwood Lincoln Continental Chrysler Imperial Dodge Challenger
# 3 3 3 3 3 3 3
# AMC Javelin Camaro Z28 Pontiac Firebird
3 3 3
length(fit$where[fit$where==3])
#[1] 17
mtcars[rownames(mtcars) %in% names(fit$where[fit$where==3]),]
# mpg cyl disp hp drat wt qsec vs am gear carb x
#Hornet 4 Drive 21.4 6 258.0 110 3.08 3.215 19.44 1 0 3 1 4
#Hornet Sportabout 18.7 8 360.0 175 3.15 3.440 17.02 0 0 3 2 5
#Valiant 18.1 6 225.0 105 2.76 3.460 20.22 1 0 3 1 6
#Duster 360 14.3 8 360.0 245 3.21 3.570 15.84 0 0 3 4 7
#Merc 240D 24.4 4 146.7 62 3.69 3.190 20.00 1 0 4 2 8
#Merc 280 19.2 6 167.6 123 3.92 3.440 18.30 1 0 4 4 10
#Merc 280C 17.8 6 167.6 123 3.92 3.440 18.90 1 0 4 4 11
#Merc 450SE 16.4 8 275.8 180 3.07 4.070 17.40 0 0 3 3 12
#Merc 450SL 17.3 8 275.8 180 3.07 3.730 17.60 0 0 3 3 13
#Merc 450SLC 15.2 8 275.8 180 3.07 3.780 18.00 0 0 3 3 14
#Cadillac Fleetwood 10.4 8 472.0 205 2.93 5.250 17.98 0 0 3 4 15
#Lincoln Continental 10.4 8 460.0 215 3.00 5.424 17.82 0 0 3 4 16
#Chrysler Imperial 14.7 8 440.0 230 3.23 5.345 17.42 0 0 3 4 17
#Dodge Challenger 15.5 8 318.0 150 2.76 3.520 16.87 0 0 3 2 22
#AMC Javelin 15.2 8 304.0 150 3.15 3.435 17.30 0 0 3 2 23
#Camaro Z28 13.3 8 350.0 245 3.73 3.840 15.41 0 0 3 4 24
#Pontiac Firebird 19.2 8 400.0 175 3.08 3.845 17.05 0 0 3 2 25
修改
如果要组织过滤类，请创建一个地图并设置为true（如果存在）。
首先创建常量：
Iterator<Transaction> iterator = transactions.iterator();
while(iterator.hasNext()) {
Transaction tx = iterator.next();
if (tx instanceof ATransaction) {
iterator.remove();
} else if (tx instanceof BTransaction) {
iterator.remove();
}
}
更新你的课程，创建一个中产阶级：
Constants.ATransaction = "ATransaction ";
Constants.BTransaction = "BTransaction ";
...
在构建时使用所需的地图填充地图：
public class MyTransaction extends Transaction {
public String baseClassName;
MyTransaction (String baseClassName) {
super();
baseClassName = baseClassName;
}
}
public class ATransaction extends MyTransaction {
ATransaction() {
super(Constants.ATransaction);
}
}
...
然后在迭代时检查它们：
Map<String, Boolean> transactionClasses = new HashMap<>();
transactionClasses.put(Constants.ATransaction, true);
transactionClasses.put(Constants.BTransaction, true);
...
答案 2 :(得分：0)
根据Determine if two Java objects are of the same class中接受的答案，答案取决于您是否寻求与t完全相同的类或其派生类。
public void remove(Transaction t) {
Iterator itr = txList.iterator();
while (itr.hasNext()) {
//if(itr.next().getClass().equals( t.getClass()) /*if the current element should be of the exact same type as t */
if(itr.next().getClass().isAssignableTo(t.getClass())) /*if the current element is allowed to be a child element of t*/
itr.remove();
}
}
另请注意，在代码的第一部分中，最好使用增强型for语句中的父Transaction类而不是Object，因为它会增强类型安全性，并且您可以从列表中删除时，不必向下转换为子类型（例如，'ATransaction'）：
for (Transaction tx : transactions) {
if (tx instanceof ATransaction) {
CustomerSession.remove(t);
} else if (tx instanceof BTransaction) {
CustomerSession.remove(t);
} else if ...
}
甚至可以用一些||而不是嵌套的if-else
来做一切