如何在Java中声明和初始化数组?
当前回答
package com.examplehub.basics;
import java.util.Arrays;
public class Array {
public static void main(String[] args) {
int[] numbers = {1, 2, 3, 4, 5};
/*
* numbers[0] = 1
* numbers[1] = 2
* numbers[2] = 3
* numbers[3] = 4
* numbers[4] = 5
*/
System.out.println("numbers[0] = " + numbers[0]);
System.out.println("numbers[1] = " + numbers[1]);
System.out.println("numbers[2] = " + numbers[2]);
System.out.println("numbers[3] = " + numbers[3]);
System.out.println("numbers[4] = " + numbers[4]);
/*
* Array index is out of bounds
*/
//System.out.println(numbers[-1]);
//System.out.println(numbers[5]);
/*
* numbers[0] = 1
* numbers[1] = 2
* numbers[2] = 3
* numbers[3] = 4
* numbers[4] = 5
*/
for (int i = 0; i < 5; i++) {
System.out.println("numbers[" + i + "] = " + numbers[i]);
}
/*
* Length of numbers = 5
*/
System.out.println("length of numbers = " + numbers.length);
/*
* numbers[0] = 1
* numbers[1] = 2
* numbers[2] = 3
* numbers[3] = 4
* numbers[4] = 5
*/
for (int i = 0; i < numbers.length; i++) {
System.out.println("numbers[" + i + "] = " + numbers[i]);
}
/*
* numbers[4] = 5
* numbers[3] = 4
* numbers[2] = 3
* numbers[1] = 2
* numbers[0] = 1
*/
for (int i = numbers.length - 1; i >= 0; i--) {
System.out.println("numbers[" + i + "] = " + numbers[i]);
}
/*
* 12345
*/
for (int number : numbers) {
System.out.print(number);
}
System.out.println();
/*
* [1, 2, 3, 4, 5]
*/
System.out.println(Arrays.toString(numbers));
String[] company = {"Google", "Facebook", "Amazon", "Microsoft"};
/*
* company[0] = Google
* company[1] = Facebook
* company[2] = Amazon
* company[3] = Microsoft
*/
for (int i = 0; i < company.length; i++) {
System.out.println("company[" + i + "] = " + company[i]);
}
/*
* Google
* Facebook
* Amazon
* Microsoft
*/
for (String c : company) {
System.out.println(c);
}
/*
* [Google, Facebook, Amazon, Microsoft]
*/
System.out.println(Arrays.toString(company));
int[][] twoDimensionalNumbers = {
{1, 2, 3},
{4, 5, 6, 7},
{8, 9},
{10, 11, 12, 13, 14, 15}
};
/*
* total rows = 4
*/
System.out.println("total rows = " + twoDimensionalNumbers.length);
/*
* row 0 length = 3
* row 1 length = 4
* row 2 length = 2
* row 3 length = 6
*/
for (int i = 0; i < twoDimensionalNumbers.length; i++) {
System.out.println("row " + i + " length = " + twoDimensionalNumbers[i].length);
}
/*
* row 0 = 1 2 3
* row 1 = 4 5 6 7
* row 2 = 8 9
* row 3 = 10 11 12 13 14 15
*/
for (int i = 0; i < twoDimensionalNumbers.length; i++) {
System.out.print("row " + i + " = ");
for (int j = 0; j < twoDimensionalNumbers[i].length; j++) {
System.out.print(twoDimensionalNumbers[i][j] + " ");
}
System.out.println();
}
/*
* row 0 = [1, 2, 3]
* row 1 = [4, 5, 6, 7]
* row 2 = [8, 9]
* row 3 = [10, 11, 12, 13, 14, 15]
*/
for (int i = 0; i < twoDimensionalNumbers.length; i++) {
System.out.println("row " + i + " = " + Arrays.toString(twoDimensionalNumbers[i]));
}
/*
* 1 2 3
* 4 5 6 7
* 8 9
* 10 11 12 13 14 15
*/
for (int[] ints : twoDimensionalNumbers) {
for (int num : ints) {
System.out.print(num + " ");
}
System.out.println();
}
/*
* [1, 2, 3]
* [4, 5, 6, 7]
* [8, 9]
* [10, 11, 12, 13, 14, 15]
*/
for (int[] ints : twoDimensionalNumbers) {
System.out.println(Arrays.toString(ints));
}
int length = 5;
int[] array = new int[length];
for (int i = 0; i < 5; i++) {
array[i] = i + 1;
}
/*
* [1, 2, 3, 4, 5]
*/
System.out.println(Arrays.toString(array));
}
}
来源于examplehub/java
其他回答
用于使用0以外的默认值进行初始化:
var arr = new int[1000];
Arrays.fill(arr, 1);
下面显示了数组的声明,但未初始化数组:
int[] myIntArray = new int[3];
下面显示了数组的声明和初始化:
int[] myIntArray = {1,2,3};
现在,下面还显示了数组的声明和初始化:
int[] myIntArray = new int[]{1,2,3};
但第三个显示了匿名数组对象创建的属性,该属性由引用变量“myIntArray”指向,因此如果我们只写“newint[]{1,2,3};”,那么这就是如何创建匿名数组对象。
如果我们只写:
int[] myIntArray;
这不是数组的声明,但以下语句使上述声明完成:
myIntArray=new int[3];
另一种声明和初始化ArrayList的方法:
private List<String> list = new ArrayList<String>(){{
add("e1");
add("e2");
}};
如果“array”是指使用java.util.Arrays,那么可以使用:
List<String> number = Arrays.asList("1", "2", "3");
// Out: ["1", "2", "3"]
这个非常简单明了。
您可以使用数组声明或数组文字(但仅当您立即声明并影响变量时,数组文字不能用于重新分配数组)。
对于基本类型:
int[] myIntArray = new int[3]; // each element of the array is initialised to 0
int[] myIntArray = {1, 2, 3};
int[] myIntArray = new int[]{1, 2, 3};
// Since Java 8. Doc of IntStream: https://docs.oracle.com/javase/8/docs/api/java/util/stream/IntStream.html
int [] myIntArray = IntStream.range(0, 100).toArray(); // From 0 to 99
int [] myIntArray = IntStream.rangeClosed(0, 100).toArray(); // From 0 to 100
int [] myIntArray = IntStream.of(12,25,36,85,28,96,47).toArray(); // The order is preserved.
int [] myIntArray = IntStream.of(12,25,36,85,28,96,47).sorted().toArray(); // Sort
对于类,例如String,它是相同的:
String[] myStringArray = new String[3]; // each element is initialised to null
String[] myStringArray = {"a", "b", "c"};
String[] myStringArray = new String[]{"a", "b", "c"};
当您首先声明一个数组,然后初始化它,将一个数组作为函数参数传递,或者返回一个数组时,第三种初始化方法非常有用。需要显式类型。
String[] myStringArray;
myStringArray = new String[]{"a", "b", "c"};
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