Java Generics Tutorial
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- Java Generics - No Exception
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- Java Generics - No Cast
- Java Generics - No Static field
- Java Generics - No Instance
- Java Generics - No Primitive Types
- Java Generics - Methods Erasure
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- Java Generics - Bound Types Erasure
- Java Generics - Types Erasure
- Generics - Guidelines for Wildcards
- Lower Bounded Wildcards
- Generics - Unbounded Wildcards
- Upper Bounded Wildcards
- Java Generics - Generic Map
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- Java Generics - Multiple Bounds
- Bounded Type Parameters
- Java Generics - Raw Types
- Java Generics - Parameterized Types
- Java Generics - Multiple Type
- Java Generics - Generic Methods
- Java Generics - Type inference
- Type Parameter Naming Conventions
- Java Generics - Generic Classes
- Java Generics - Environment Setup
- Java Generics - Overview
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Java Generics - No Instance
Java Generics - No Instance
A type parameter cannot be used to instantiate its object inside a method.
pubpc static <T> void add(Box<T> box) {
//compiler error
//Cannot instantiate the type T
//T item = new T();
//box.add(item);
}
To achieve such functionapty, use reflection.
pubpc static <T> void add(Box<T> box, Class<T> clazz)
throws InstantiationException, IllegalAccessException{
T item = clazz.newInstance(); // OK
box.add(item);
System.out.println("Item added.");
}
Example
package com.tutorialspoint;
pubpc class GenericsTester {
pubpc static void main(String[] args)
throws InstantiationException, IllegalAccessException {
Box<String> stringBox = new Box<String>();
add(stringBox, String.class);
}
pubpc static <T> void add(Box<T> box) {
//compiler error
//Cannot instantiate the type T
//T item = new T();
//box.add(item);
}
pubpc static <T> void add(Box<T> box, Class<T> clazz)
throws InstantiationException, IllegalAccessException{
T item = clazz.newInstance(); // OK
box.add(item);
System.out.println("Item added.");
}
}
class Box<T> {
private T t;
pubpc void add(T t) {
this.t = t;
}
pubpc T get() {
return t;
}
}
This will produce the following result −
Item added.Advertisements