如何在 Java 中打印集合中的内容
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How to print content in Collection in Java
提问by Panadol Chong
Good day All,
大家好，
Normally, I will print all the content in List by look the list.size()and assign it to an object and print the object value. The following is my example code:
通常，我会通过查看列表中的所有内容list.size()并将其分配给一个对象并打印对象值。以下是我的示例代码：
List ccUserList = new ArrayList(); // Here I declare a List
Collection ccGroupCol = new ArrayList(); // Here I declare a collection
CCuserBO bo = null;
ccUserList = getSummaryList();
for(int i = 0, i < ccUserList.size() , i++){
bo = ( CCUserBO ) ccUserList.get(i);
System.out.println(bo.userName);
}
I would like to ask about the way to print content in Collection. Since Collection no have .get() function.
我想问一下在Collection中打印内容的方式。由于 Collection 没有 .get() 函数。
The following in the code that I try in Collection:
我在 Collection 中尝试的代码中的以下内容：
CCuserBO newBo = null;
ccGroupCol = getSummaryList();
Iterator iterator = ccGroupCol.iterator();
while ( iterator.hasNext()){
newBo = iterator.next(); //error here, Type mismatch: cannot convert from Object to //Object[]
System.out.println("....");
}
回答by Panadol Chong
I found the solution. Here is the example code:
我找到了解决方案。这是示例代码：
CCGroupBO newBo;
for(int i = 0 ; i < ccGroupCol.size() ; i++){
newBo = ( CCGroupBO ) ccGroupCol.toArray()[i];
System.out.println(newBo.getGroupName());
}
Thanks for all your help.
感谢你的帮助。
回答by Shailesh Saxena
If you simply want to print all elements of a Collection just sysout Collection directly it will provide you the following form in output: [element1, element2, ....] because toString() method is overrided and implemented to provide such output for all Collection classses.
如果您只是想直接打印集合的所有元素，只需直接 sysout 集合，它将在输出中为您提供以下形式：[element1, element2, ....] 因为 toString() 方法被覆盖并实现为所有提供此类输出收藏类。
By using Iterator you can get the element one by one:
通过使用 Iterator 可以一一获取元素：
Iterator iterator = ccGroupCol.iterator();
while ( iterator.hasNext()){
newBo = (**type cast here to particular newBo object type**)iterator.next();
System.out.println(newBo);//here whatever you implemented in toString() method
// in newBo type class(if you did so), you will get that type of output, if you do not override
//toString() to provide your implementation,you will get default implementation in
//which it will show <the object class>@<its hash code>
}
Note: the return type of iterator.next() is Object type, so you must type cast it to avoid incompatible type exception. Or use Generics.
注意：iterator.next() 的返回类型是 Object 类型，所以你必须对它进行类型转换以避免不兼容的类型异常。或者使用泛型。
回答by Pradeep Kr Kaushal
You can use the for loop to iterate the collection.
您可以使用 for 循环来迭代集合。
Collection collection= new ArrayList();
for (Object obj : collection) {
//Here you can type cast the obj then you can print.
}
回答by Jan
As statet in comment, a faster solution for your own answer:
正如评论中的陈述，您自己的答案的更快解决方案：
Collection<CCGroupBO> ccGroupCol = new ArrayList<CCGroupBO>()
…
CCGroupBO[] boArray = ccGroupCol.toArray();
for(CCGroupBO newBo : boArray){
System.out.println(newBo.getGroupName());
}
or even more direct:
甚至更直接：
Collection<CCGroupBO> ccGroupCol = new ArrayList<CCGroupBO>()
…
for(CCGroupBO newBo : ccGroupCol){
System.out.println(newBo.getGroupName());
}
depending on other circumstances there is even a nicer method:
根据其他情况，还有更好的方法：
class CCGroupBO {
…
public String toString() {
return getGroupName();
}
}
…
Collection<CCGroupBO> ccGroupCol = new ArrayList<CCGroupBO>()
…
System.out.println(ccGroupCol);
