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 

  null

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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:

1. Basic type (numeric type): 0

2. Basic type (boolean): false

3. Basic type (char type): (char) 0

4. 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 

  null

Copy after login

Copy 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:

1. Basic type (numeric type): 0

2. Basic type (boolean): false

3. Basic type (char type): (char) 0

4. Object type: nul