java面试常见问题

反射

泛型

• 目的：参数化类型
• 用法：泛型类、泛型接口、泛型方法
  • 泛型类

    // 简单范型
    class Test<T> {
      private T var;
      public T getVar() {
        return var;
      }
      public void setVar(T var) {
        this.var = var;
      }
    } 
    // 多元泛型
    class TestKV<K,V> {
      private K key;
      private V value;
      public K getKey() {
        return key;
      }
      public void setKey(K key) {
        this.key = key;
      }
      public V getValue() {
        return value;
      }
      public void setValue(V value) {
        this.value = value;
      }
    }
    
    public class Demo {
      public static void main(String[] args) {
        Test<String> test = new Test<String>();
        test.setVar("aa");
        System.out.println(test.getVar());
    
        TestKV<String, String> testKV = new TestKV<String, String>();
        testKV.setKey("hello");
        testKV.setValue("world");
        System.out.println(testKV.getKey() +":"+testKV.getValue());
      }
    }

  • 泛型接口

    interface Test<T> {
      public T getVar();
    }
    class TestImpl<T> implement Test<T> {
      private T var;
      public TEstImpl(T var) {
        this.var = var;
      }
      public T getVar() {
        return var;
      }
      public void setVar(T var) {
        this.var = var;
      }
    }
    public class Demo{
      public static void main(String[] args) {
        Test<String> test = new TestImpl<String>("tom");
        System.out.pringln(test.getVar());
      }
    }

  • 泛型方法

    public class Demo {
      public <T> T getObject(Class<T> c) {
        T t = c.newInstance();
        retrun t;
      }
    }

注解