如何处理Java的ArrayList的refrerences和任务？ [英] How does Java handle ArrayList refrerences and assignments?

问题描述

我主要是用C编写，但我使用Java这个项目。我想知道什么是Java的引擎盖下在这里干什么。

I mostly write in C but am using Java for this project. I want to know what Java is doing here under the hood.

ArrayList<Integer> prevRow, currRow;
currRow = new ArrayList<Integer>();
for(i =0; i < numRows; i++){
    prevRow = currRow;
    currRow.clear();
    currRow.addAll(aBunchOfItems);
}

是prevRow = currRow行复制列表还是prevRow现在指向同一个列表，currRow？如果prevRow指向同一列表作为currRow，我应该创建一个新的ArrayList，而不是结算的....

Is the prevRow = currRow line copying the list or does prevRow now point to the same list as currRow? If prevRow points to the same list as currRow, I should create a new ArrayList instead of clearing....

private ArrayList<Integer> someFunction(ArrayList<Integer> l){
    Collections.sort(l);
    return l;
}

main(){
    ArrayList<Integer> list = new ArrayList<Integer>(Integer(3), Integer(2), Integer(1));

    list = someFunction(list);  //Option 1
    someFunction(list);  //Option 2
}

在一个类似的问题，做方案1和方案2在上面做code是一回事吗？

In a similar question, do Option 1 and Option 2 do the same thing in the above code?

谢谢 -

乔纳森

推荐答案

如果你来的Java从C / C ++记住这条黄金法则可以回答几乎所有的这些疑惑：Java中的一个变量（除了基本类型）是的始终参考（排序的指针）一个对象，本身从来不是一个对象。

If you come to Java from C/C++ remember this golden rule which will answer almost all these doubts: in Java a variable (except primitives) is always a reference (sort of pointer) to an object, never an object in itself.

例如

 prevRow = currRow;

被分配一个参考，使prevRow和currRow现在指代相同的对象。对象不复制，无论是在分配，也不在参数传递（被复制/分配为基准）。等等。

is assigning a reference, so that prevRow and currRow now refer to the same object. Objects are not copied, neither in assignments, nor in argument passing (what is copied/assigned is the reference). And so on.

这篇关于如何处理Java的ArrayList的refrerences和任务？的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！