Java 中数组赋值的有趣事实
原文:https://www . geesforgeks . org/interior-facts-array-assignment-Java/
前提条件:Java 中的数组
在处理数组时，我们必须完成 3 项任务，即声明、创建、初始化或赋值。 数组声明:
int[] arr;
创建数组:
// Here we create an array of size 3
int[] arr = new int[3];
数组初始化:
arr[0] = 1;
arr[1] = 2;
arr[3] = 3;
int intArray[]; // declaring array
intArray = new int[20]; // allocating memory to array
给数组赋值时的一些重要事实:
-
For primitive data types : In case of primitive type arrays, as array elements we can provide any type which can be implicitly promoted to the declared type array. Apart from that, if we are trying to use any other data-types then we will get compile-time error saying possible loss of precision.
java // Java program to illustrate the concept of array // element assignments on int type array public class Test { public static void main(String[] args) { int[] arr = new int[3]; arr[0] = 1; arr[1] = 'a'; byte b = 10; arr[2] = b; System.out.println(arr[0] + arr[1] + arr[2]); } }输出:
```java 108
```
```java // Java program to illustrate the concept of array // element assignments on int type array public class Test { public static void main(String[] args) { int[] arr = new int[3];
// Assigning long value to int type. arr[0] = 10l; arr[1] = 'a'; byte b = 10; arr[2] = b;
System.out.println(arr[0] + arr[1] + arr[2]); } } ```
输出:
```java possible loss of precision.
```
```java // Java program to illustrate the concept of array // element assignments on char type array public class Test { public static void main(String[] args) { char[][] arr = new char[2][2];
// Assigning long value to int type. arr[0][0] = 10l; arr[0][1] = 'a'; char b = 10; arr[1][0] = b;
// Assigning double value to char type arr[1][1] = 10.6; } } ```
输出:
```java error: incompatible types: possible lossy conversion from long to char error: incompatible types: possible lossy conversion from double to char
```
-
Object type Arrays : If we are creating object type arrays then the elements of that arrays can be either declared type objects or it can be child class object.
java // Java program to illustrate the concept of array // element assignments on Number type array public class Test { public static void main(String[] args) { Number[] num = new Number[2]; num[0] = new Integer(10); num[1] = new Double(20.5); System.out.println(num[0]); System.out.println(num[1]); } }输出:
```java 10 20.5
```
```java // Java program to illustrate the concept of array // element assignments on Number type array public class Test { public static void main(String[] args) { Number[] num = new Number[3]; num[0] = new Integer(10); num[1] = new Double(20.5);
// Here String is not the child class of Number class. num[2] = new String(“GFG”); } } ```
输出:
```java Compile-time error(incompatible types)
```
```java // Java program to illustrate the concept of array // element assignments on Number type array public class Test { public static void main(String[] args) { Number[][] arr = new Number[2][2]; arr[0][0] = 10l;
// Assigning char to Number type array arr[0][1] = 'a'; byte b = 10; arr[1][0] = b;
// Assigning String to Number type array arr[1][1] = "GEEKS"; } } ```
输出:
```java error: incompatible types: char cannot be converted to Number error: incompatible types: String cannot be converted to Number
```
-
Interface type array : For interface type array, we can assign elements as its implementation class objects.
```java // Java program to illustrate the concept of array // element assignments on Interface type array public class Test { public static void main(String[] args) { Runnable[] run = new Runnable[2];
// Thread class implements Runnable interface. run[0] = new Thread(); run[1] = new Thread(); } } ```
```java // Java program to illustrate the concept of array // element assignments on Interface type array public class Test { public static void main(String[] args) { Runnable[] run = new Runnable[2]; run[0] = new Thread();
// String class does not implements Runnable interface. run[1] = new String(“GFG”); } } ```
输出:
```java Compile-time error(Incompatible types)
```
解释:在上面的程序中，我们给出了导致编译时错误的 String 类的元素。因为我们知道 String 不实现 Runnable 接口。
参考:https://docs . Oracle . com/javase/specs/jls/se7/html/jls-10 . html
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