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 itdynamic definitionhere.

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 aaddress reference. Line 4 outputs the real array value because it has been converted byArrays.toString(). For Java beginners,references and valuesstill 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 adynamic linked list, we canadd, 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 arrayList = new ArrayList(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 toListf7e83be87db5cd2d9a8a0b8117b38cd4, so that you can use thecontains functionof 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

##ArrayUtilsis thearray processing class libraryprovided byApache, itsaddAll methodcan 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 thejoin methodinStringUtils, 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 asset type, which is mainly used in display lists. You can also convert Array to List first, and then convert List to Set.

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

8. Array flipping

Use Apache’s

ArrayUtils tool classThe .reverse() method inArray 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’sArrayUtils tool class#removeElement() method inRemoves 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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