当您在编译时使用E时，您并不真正关心实际的泛型类型“E”(无论是使用反射还是使用泛型类型的基类)，因此让子类提供E的实例。

abstract class SomeContainer<E>
{
    abstract protected E createContents();
    public void doWork(){
        E obj = createContents();
        // Do the work with E 
     }
}

class BlackContainer extends SomeContainer<Black>{
    protected Black createContents() {
        return new Black();
    }
}

对诺亚的回答进行了改进。

改变的原因

a]如果使用多于一个泛型类型，则更安全，以防您更改顺序。

b]类泛型类型签名会不时变化，这样你就不会对运行时中无法解释的异常感到惊讶。

健壮的代码

public abstract class Clazz<P extends Params, M extends Model> {

    protected M model;

    protected void createModel() {
    Type[] typeArguments = ((ParameterizedType) this.getClass().getGenericSuperclass()).getActualTypeArguments();
    for (Type type : typeArguments) {
        if ((type instanceof Class) && (Model.class.isAssignableFrom((Class) type))) {
            try {
                model = ((Class<M>) type).newInstance();
            } catch (InstantiationException | IllegalAccessException e) {
                throw new RuntimeException(e);
            }
        }
    }
}

或者使用一个眼线笔

一行代码

model = ((Class<M>) ((ParameterizedType) this.getClass().getGenericSuperclass()).getActualTypeArguments()[1]).newInstance();

你可以通过下面的代码片段来实现这一点:

import java.lang.reflect.ParameterizedType;

public class SomeContainer<E> {
   E createContents() throws InstantiationException, IllegalAccessException {
      ParameterizedType genericSuperclass = (ParameterizedType)
         getClass().getGenericSuperclass();
      @SuppressWarnings("unchecked")
      Class<E> clazz = (Class<E>)
         genericSuperclass.getActualTypeArguments()[0];
      return clazz.newInstance();
   }
   public static void main( String[] args ) throws Throwable {
      SomeContainer< Long > scl = new SomeContainer<>();
      Long l = scl.createContents();
      System.out.println( l );
   }
}

如果你在泛型类中需要一个类型参数的新实例，那么让你的构造函数要求它的类…

public final class Foo<T> {

    private Class<T> typeArgumentClass;

    public Foo(Class<T> typeArgumentClass) {

        this.typeArgumentClass = typeArgumentClass;
    }

    public void doSomethingThatRequiresNewT() throws Exception {

        T myNewT = typeArgumentClass.newInstance();
        ...
    }
}

用法:

Foo<Bar> barFoo = new Foo<Bar>(Bar.class);
Foo<Etc> etcFoo = new Foo<Etc>(Etc.class);

优点:

比Robertson的超级类型令牌(STT)方法简单得多(而且问题更少)。 比STT方法更有效(STT方法会把你的手机当早餐吃)。

缺点:

Can't pass Class to a default constructor (which is why Foo is final). If you really do need a default constructor you can always add a setter method but then you must remember to give her a call later. Robertson's objection... More Bars than a black sheep (although specifying the type argument class one more time won't exactly kill you). And contrary to Robertson's claims this does not violate the DRY principal anyway because the compiler will ensure type correctness. Not entirely Foo<L>proof. For starters... newInstance() will throw a wobbler if the type argument class does not have a default constructor. This does apply to all known solutions though anyway. Lacks the total encapsulation of the STT approach. Not a big deal though (considering the outrageous performance overhead of STT).

你能做的就是——

首先声明该泛型类的变量 2.然后创建它的构造函数并实例化该对象 那就在任何你想用的地方用吧

的例子,

1

私有类<E>实体;

2

public xyzservice(Class<E> entity) {
        this.entity = entity;
    }



public E getEntity(Class<E> entity) throws InstantiationException, IllegalAccessException {
        return entity.newInstance();
    }

3.

E E = getEntity(实体);

package org.foo.com;

import java.lang.reflect.ParameterizedType;
import java.lang.reflect.Type;

/**
 * Basically the same answer as noah's.
 */
public class Home<E>
{

    @SuppressWarnings ("unchecked")
    public Class<E> getTypeParameterClass()
    {
        Type type = getClass().getGenericSuperclass();
        ParameterizedType paramType = (ParameterizedType) type;
        return (Class<E>) paramType.getActualTypeArguments()[0];
    }

    private static class StringHome extends Home<String>
    {
    }

    private static class StringBuilderHome extends Home<StringBuilder>
    {
    }

    private static class StringBufferHome extends Home<StringBuffer>
    {
    }   

    /**
     * This prints "String", "StringBuilder" and "StringBuffer"
     */
    public static void main(String[] args) throws InstantiationException, IllegalAccessException
    {
        Object object0 = new StringHome().getTypeParameterClass().newInstance();
        Object object1 = new StringBuilderHome().getTypeParameterClass().newInstance();
        Object object2 = new StringBufferHome().getTypeParameterClass().newInstance();
        System.out.println(object0.getClass().getSimpleName());
        System.out.println(object1.getClass().getSimpleName());
        System.out.println(object2.getClass().getSimpleName());
    }

}