反射-访问构造方法

最新推荐文章于 2024-12-21 00:38:29 发布

原创最新推荐文章于 2024-12-21 00:38:29 发布 · 261 阅读

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CC 4.0 BY-SA版权

本文通过一个具体的Java类示例，详细介绍了不同构造方法的定义及其使用方式，并通过反射API展示了如何获取并实例化这些构造方法，同时分析了它们的参数类型、异常处理以及可变参数的支持情况。

创建一个类：

public class Example_01 {
	String s;
	int i,i2,i3;
	private Example_01(){
		
	}
	protected Example_01(String s,int i){
		this.s = s;
		this.i = i;
	}
	public Example_01(String...strings)throws NumberFormatException{
		if(0< strings.length)
			i = Integer.valueOf(strings[0]);
		if(0< strings.length)
			i2 = Integer.valueOf(strings[1]);
		if(0< strings.length)
			i3 = Integer.valueOf(strings[2]);
	}
	public void print(){
		System.out.println("s=" +s);
		System.out.println("i=" +i);
		System.out.println("i2=" +i2);
		System.out.println("i3=" +i3);
	}

}

编写测试类：

public class Text{
	
	public static void main(String args[]){
		Example_01 example = new Example_01();
		Class exampleC = example.getClass();
		Constructor[] declaredConstructors = exampleC.getDeclaredConstructors();
		for (int i = 0; i < declaredConstructors.length; i++) {
			Constructor constructor = declaredConstructors[i];
			System.out.println("查看是否允许带有可变数量的参数：" + constructor.isVarArgs());
			System.out.println("该构造方法的入口参数类型依次为：");
			Class[] parameterTypes = constructor.getParameterTypes();
			for (int j = 0; j < parameterTypes.length; j++) {
				System.out.println("" + parameterTypes[j]);
			}
			System.out.println("该构造方法可能抛出的异常类型为：");
			Class[] exceptionTypes = constructor.getExceptionTypes();
			for (int j = 0; j < exceptionTypes.length; j++) {
				System.out.println("" + exceptionTypes[j]);
			}
			Example_01 example2 = null;
			while (example2 == null) {
				try {
					if(i== 2){
						example2 = (Example_01)constructor.newInstance();
					}else if(i == 1){
						example2 = (Example_01)constructor.newInstance("7",5);
					}else{
						Object[] parameters = new Object[]{new String[]{"100","200","300"}};
						example2 = (Example_01) constructor.newInstance(parameters);
					}
				} catch (Exception e) {
					e.printStackTrace();
					System.out.println("在创建对象时抛出异常，下面执行setAccessible()方法");
					constructor.setAccessible(true);
				}
			}
			example2.print();
			System.out.println();
		}
	}
}

输出效果：