在 Java 中的 arrayList 中增加整数的最佳方法
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Best way to increment Integer in arrayList in Java
提问by WVrock
What is the cleanest way to increment an Integer in an ArrayList?
在 ArrayList 中增加 Integer 的最简洁方法是什么？
ArrayList<Integer> ints = new ArrayList<>();
ints.add(5);
ints.add(9);
What is the cleanest way to increment the last element?
增加最后一个元素的最干净的方法是什么？
ints.set(ints.size() - 1, ints.get(ints.size() - 1) + 1);seems pretty ugly to me.
ints.set(ints.size() - 1, ints.get(ints.size() - 1) + 1);对我来说似乎很丑。
采纳答案by ursa
Maybe you need to use another structure of data?
也许您需要使用另一种数据结构？
LinkedList<AtomicInteger> list = new LinkedList<AtomicInteger>();
ints.add(new AtomicInteger(5));
ints.add(new AtomicInteger(9));
list.getLast().incrementAndGet();
回答by Sotirios Delimanolis
You can't increment the value in place since Integerobjects are immutable. You'll have to get the previous value at a specific position in the ArrayList, increment the value, and use it to replace the old value in that same position.
由于Integer对象是不可变的，因此您不能就地增加值。您必须在 中的特定位置获取先前的值ArrayList，增加该值，并使用它来替换同一位置的旧值。
int index = 42; // whatever index
Integer value = ints.get(index); // get value
value = value + 1; // increment value
ints.set(index, value); // replace value
Alternatively, use a mutable integer type, like AtomicInteger(or write your own).
或者，使用可变整数类型，例如AtomicInteger（或编写您自己的）。
回答by evernoob
I have done something like this:
我做了这样的事情：
arraylistofint.set(index, arraylistofint.get(index) + 1);
here is an example from my code (modified names):
这是我的代码中的一个示例（修改后的名称）：
ArrayList<Integer> numBsPerA = new ArrayList<> ();
...
int cntAs = 0;
int cntBs = 0;
for ( TypeA a : AnArrayListOfAs )
{
numBsPerA.add(0);
for ( TypeB b : a.getAnArrayListOfBs() )
{
numBsPerA.set(cntAs, numBsPerA.get(cntAs) + 1);
cntBs++;
}
System.out.println(a.toString()+ " has "
+numBsPerA.get(cntAs)+" TypeBs");
cntAs++;
}
System.out.println("Total number of As: "+cntAs);
System.out.println("Total number of Bs: "+cntBs);
// can now loop over numBsPerA to check how many Bs per A or whatever.
回答by KEERTHAN SHETTY
I can done by the code using java ...In that we can Increment each element of the list
我可以通过使用 java 的代码来完成......因为我们可以增加列表的每个元素
List<Integer> list= new ArrayList<Integer>();
//int[] primitive = List1.toArray(list1);
int count=0;
int count1=0;
int k=0;
list.add(3);list.add(2);list.add(3);list.add(5);
System.out.println("The given input is");
for(int i:list){
System.out.println(i);
}
Integer[] a = list.toArray(new Integer[list.size()]);
for(int i = 0; i <a.length; i++)
{
if(i==a.length-1){
a[i]++;
count++;
}else if(i==a.length-2){
a[i]++;
count++;
}else if(i==a.length-3){
a[i]++;
count++;
}else if(i==a.length-4){
a[i]++;
count++;
}
}
System.out.println("After first operation");
for(int i:a){
System.out.println(i);
}
System.out.println("the first count is"+count);
for(int i = 0; i <a.length; i++)
{
if(i==a.length-1){
a[i]--;
count1++;
}else if(i==a.length-2){
a[i]--;
count1++;
}else if(i==a.length-3){
a[i]--;
count1++;
}else if(i==a.length-4){
a[i]--;
count1++;
}
}
for(int i:a){
System.out.println(i);
}
System.out.println("the second count is"+count1);
//int Count2=count+count1;
System.out.println("After second operation");
System.out.println("--------------------------------------------");
for(int j:a){
System.out.println(j);
}
List<Integer> list1=Arrays.asList(a);
System.out.println("After conversion of list");
for(int i:list1){
System.out.println(i);
}
i made the count also...
我也算了……
This question asked in one of the interview also..
在其中一次采访中也问到了这个问题。
