java—Constructing an array with generic parameter types
I suddenly thought of a question when I was coding a while ago. Usually our array is passed into the method as a parameter. What if we want to create an array in the method? When the type is clear, this is not difficult. What if the parameters we pass in are parameters of a generic type?
public static <T> T[] creArray (T obj){
T[] arr = new T[10];
}The above method of using T to create a new array directly is wrong, and an error will appear during compilation: Cannot create a generic array of T.. Java does not support directly creating arrays of unknown types.
Finally I got such a perfect solution:
package Test;import java.lang.reflect.Array;/**
*
* @author QuinnNorris
* 在泛型方法中创建泛型类型的数组
*/public class Test {
public static void main(String[] args) { // TODO Auto-generated method stub
String a = "ccc";//创建一个String，作为泛型类型
String[] ar = creArray(a); for(String art :ar)//循环打印
System.out.println(art);
} //泛型静态方法
public static <T> T[] creArray (T obj){
T[] arr = (T[])Array.newInstance(obj.getClass(), 5);
arr[1] = obj;
System.out.println(arr[1]); return arr;
}
}The code output is as follows:
ccc //方法中输出的arr[1] null //以下5个是main中循环迭代出的数组值 ccc null null nullCopy after loginCopy after login
The above method is completely feasible. We construct an array of a specifiable type by using the newInstance method of the Array class. It should also make sense to use reflection to do this job. Because the generic type T can only be determined at runtime, we must find a way to create a generic array at Java runtime. The only technology that works at Java runtime is reflection.
I also saw null, so I would like to sort out the values of different types of array initialization in Java:
Basic type (numeric type): 0
Basic type (boolean): false
Basic type (char type): (char) 0
Object type: null
I suddenly thought of a problem when I was coding a while ago. Usually our array is passed into the method as a parameter. What if we want to create an array in the method? When the type is clear, this is not difficult. What if the parameters we pass in are parameters of a generic type?
public static <T> T[] creArray (T obj){
T[] arr = new T[10];
}The above method of using T to directly create a new array is wrong, and an error will appear during compilation: Cannot create a generic array of T.. Java does not support directly creating arrays of unknown types.
Finally I got such a perfect solution:
package Test;import java.lang.reflect.Array;/**
*
* @author QuinnNorris
* 在泛型方法中创建泛型类型的数组
*/public class Test {
public static void main(String[] args) { // TODO Auto-generated method stub
String a = "ccc";//创建一个String，作为泛型类型
String[] ar = creArray(a); for(String art :ar)//循环打印
System.out.println(art);
} //泛型静态方法
public static <T> T[] creArray (T obj){
T[] arr = (T[])Array.newInstance(obj.getClass(), 5);
arr[1] = obj;
System.out.println(arr[1]); return arr;
}
}The code output is as follows:
ccc //方法中输出的arr[1] null //以下5个是main中循环迭代出的数组值 ccc null null nullCopy after loginCopy after login
The above method is completely feasible. We construct an array of a specifiable type by using the newInstance method of the Array class. It should also make sense to use reflection to do this job. Because the generic type T can only be determined at runtime, we must find a way to create a generic array at Java runtime. The only technology that can work at Java runtime is reflection.
I also saw null, so I would like to sort out the values of different types of array initialization in Java:
Basic type (numeric type): 0
Basic type (boolean): false
Basic type (char type): (char) 0
Object type: nul
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