Common operations on java arrays

1. Define a Java array

There are three ways to define an array.

The first is to define an array and specify the length of the array. We call it dynamic definition here.

The second is to directly initialize the array content

The third is to initialize the value while allocating memory space.

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

2. Print elements in Java array

In Java There is a difference between array references and values. The third line prints intArray directly, and the output is garbled, because intArray is just a address reference . Line 4 outputs the real array value because it has been converted by Arrays.toString(). For Java beginners, references and values still need to be paid attention to.

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. Create ArrayList from Array

Why should we convert Array into What about ArrayList? It may be because ArrayList is a dynamic linked list, we can add, delete, and modify ArrayList more conveniently. We do not need to loop Array to add each element to ArrayList. Use the following code Conversion can be easily achieved.

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. Check whether the array contains a certain value

Use firstArrays.asList()Convert Array to List, so that you can use the contains function of the dynamic linked list to determine whether the element is included in the linked list.

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

5. Connect two arrays

##ArrayUtils is the array processing class library provided by Apache, its addAll method can easily connect two arrays into one array.

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

6. Output the elements in the array as strings

Similarly, using the join method in StringUtils, the elements in the array can be output in the form of a 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. Convert Array into Set collection

##In Java Using

Set, you can easily save the required type in a variable as set type, which is mainly used in display lists. You can also convert Array to List first, and then convert List to Set.

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

8. Array flipping

Use Apache’s

ArrayUtils tool class The .reverse() method in Array reversal method. You can also specify the starting and ending reverse positions.

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

9. Remove an element from the array

Use Apache’s ArrayUtils tool class#removeElement() method in Removes the first occurrence of the specified element from the array and returns a new array

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

Original article address: https://www.jianshu.com/p/9a9c3042fb29

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