addAll(Collection<? extends E>c): This method appends all the elements from the given collection to the end of the list. The order of insertion depends on the order in which the collection iterator returns them. addAll(intindex, Collection<? extends E>c): we can use this method to ins...
Here, we have used theaddAll()method to add all the elements of the hashset to the arraylist. The optionalindexparameter is not present in the method. Hence, all elements are added at the end of the arraylist.
[1]ArrayList<T> al=new ArrayList<T>();指定集合元素只能是T类型 [2]ArrayList<?> al=new ArrayList<?>();集合元素可以是任意类型,这种没有意义,一般是方法中,只是为了说明用法 [3]ArrayList<? extends E> al=new ArrayList<? extends E>(); 泛型的限定: ? extends E:接收E类型或者E的子类型。 ?su...
1. ArrayList addAll() Method TheaddAll()method first ensures that there is sufficient space in the list. If the list does not have space, then it grows the list by adding more spaces in the backing array. ThenaddAll()appends new elements to the end of the list or at the specified i...
import java.io.*;import java.util.ArrayList;import java.util.Arrays;import java.util.TreeSet;public class TextFile extends ArrayList<String> { public static String read(String fileName) { StringBuilder stringBuilder = new StringBuilder(); try { BufferedReader in = new BufferedReader(new FileReader...
Attempt to invoke interface method 'boolean java.util.List.add(java.lang.Object)' on a null object reference 2018-02-26 20:56 −尝试在一个空的对象引用上引用boolean java.util.List.add()这个方法; 错误例子: private ArrayList<String> classList; classList.add("2014211501"); 相当于classList为...
在stackoverflow上看到的一篇回答,老外真是太professional了,mark一下。最后的summary值得看一下。 TheJava API docs saythe following aboutCollections.addAll The behavior of this convenience method is identical to that of c.addAll(Arrays.asList(elements)), but this method is likely to run significantly...
这将失败，并显示与您所描述的相同的错误。按照这些思路尝试一些方法来修复它。
util.ArrayList; public class GFG { public static void main(String args[]) { // Creating an empty Stack Stack<String> stack = new Stack<String>(); // Use add() method to add elements in the Stack stack.add("Geeks"); stack.add("for"); stack.add("Geeks"); stack.add("10"); ...
* element returned by the iterator in turn to see if it's contained * in the specified collection. If it's so contained, it's removed from * this collection with the iterator's remove method. * * Note that this implementation will throw an * UnsupportedOperation...