[Java基础] 数组

2013 十月 10 周四 Zoey Young Java Java 编程基础

这回笔试, 要手写代码, 然后发现很久不写Java, 连怎么初始化数组都不记得啦. 方括号? 大括号? 要不要写大小? 在哪写? 主要也是受了Python列表的影响...

The following are top 10 methods for Java Array. They are the most voted questions from stackoverflow.

0. Declare an array

String[] aArray = new String[5];
String[] bArray = {"a", "b", "c", "d", "e"};
String[] cArray = new String[]{"a","b","c","d","e"};

【数组长度: arr.length, 不是size, 也不是len】

1. Print an array in Java

int[] intArray = { 1, 2, 3, 4, 5 };
String intArrayString = Arrays.toString(intArray);

// print directly will print reference value
System.out.println(intArray);
// [I@7150bd4d

System.out.println(intArrayString);
// [1, 2, 3, 4, 5]

2. Create an ArrayList from an array

String[] stringArray = {"a", "b", "c", "d", "e"};
ArrayList<String> arrayList = new ArrayList<String>(Arrays.asList(stringArray));
System.out.println(arrayList);
// [a, b, c, d, e]

3. Check if an array contains a certain value

String[] stringArray = {"a", "b", "c", "d", "e"};
boolean b = Arrays.asList(stringArray).contains("a");
System.out.println(b);
// true

4. Concatenate two arrays

int[] intArray = { 1, 2, 3, 4, 5 };
int[] intArray2 = { 6, 7, 8, 9, 10 };
// Apache Commons Lang library
int[] combinedIntArray = ArrayUtils.addAll(intArray, intArray2);

5. Declare an array inline

method(new String[]{"a", "b", "c", "d", "e"});

6. Joins the elements of the provided array into a single String

// containing the provided list of elements
// Apache common lang
String j = StringUtils.join(new String[] { "a", "b", "c" }, ", ");
System.out.println(j);
// a, b, c

7. Covnert an ArrayList to an array

String[] stringArray = { "a", "b", "c", "d", "e" };
ArrayList<String> arrayList = new ArrayList<String>(Arrays.asList(stringArray));
String[] stringArr = new String[arrayList.size()];
arrayList.toArray(stringArr);
for (String s : stringArr)
    System.out.println(s);

8. Convert an array to a set

Set<String> set = new HashSet<String>(Arrays.asList(stringArray));
System.out.println(set);
//[d, e, b, c, a]

9. Reverse an array

int[] intArray = {1, 2, 3, 4, 5};
ArrayUtils.reverse(intArray);
System.out.println(Arrays.toString(intArray));
//[5, 4, 3, 2, 1]

10. Remove element of an array

int[] intArray = { 1, 2, 3, 4, 5 };
int[] removed = ArrayUtils.removeElement(intArray, 3);//create a new array
System.out.println(Arrays.toString(removed));
One more – convert int to byte array

byte[] bytes = ByteBuffer.allocate(4).putInt(8).array();

for (byte t : bytes) {
   System.out.format("0x%x ", t);
}

One more – convert int to byte array

byte[] bytes = ByteBuffer.allocate(4).putInt(8).array();
for (byte t : bytes) {
   System.out.format("0x%x ", t);
}