使用循环从另一个数组创建一个数组

Question

I am Passing an Array into a for loop with an if statment, I am want to have all the elements that evaluate true be added to a new array. How Do I do This?

Answer 1

Supposing you have an object array, and you want to create a possibly smaller array containing the elements that satisfy some predicate, you are faced with the problem of knowing how big to make the new array. You can determine that only by testing each starting element against the predicate, which you would normally prefer to avoid doing twice. One way to approach the problem would be to use a List to temporarily hold the elements you want to collect:

MyElementType[] myArray = { /* ... */ };
MyElementType[] result;
List<MyElementType> temp = new ArrayList<MyElementType>();

for (MyElementType element : myArray) {
    if (passesMyTest(element)) {
        temp.add(element);
    }
}

result = temp.toArray(new MyElementType[0]);

Of course, it's usually easier to work directly with List s instead of with arrays, but sometimes you don't have that luxury.