Java 数组

1.  声明一个数组 

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

2.  输出一个数组 

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]

3.  从一个数组创建数组列表 

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]

4.  检查一个数组是否包含某个值 

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

5.  连接两个数组 

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

6.  声明一个内联数组（Array inline） 

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

7.  把提供的数组元素放入一个字符串 

// 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

8.  将一个数组列表转换为数组 

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);

9.  将一个数组转换为集（set） 

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

10.  逆向一个数组 

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

11.  移除数组中的元素 

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

12. 自定义类型的数组

public static void main(String[] args)
    {
        Student []s = new Student[10];
        for (int i=0 ;i<10;i++){
            s[i].setM_name("T");
        }
    }
//以上写法有问题，这样只初始化了数组的位置，没初始化数组对应的对象，会出现空指针异常。
//正确写法：
Student []s = {new Student(),new Student(),new Student(),new Student(),new Student(),new Student(),new Student(),new Student(),new Student(),new Student()};
for (int i=0 ;i<10;i++){
    s[i].setM_name("T");
}

//还遇到一个比较好玩的问题，这样写：
Student ss = new Student();
Student []s = {ss,ss,ss,ss,ss,ss,ss,ss,ss};
for (int i=0 ;i<10;i++){
    s[i].setM_name("T");
}
//这样写的时候整个数组都指向了同一个位置。