Java從入門到精通閱讀筆記（第4版）19

反射

1.訪問構造方法

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 (1 < strings.length)
			i2 = Integer.valueOf(strings[1]);
		if (2 < 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);
	}
}

import java.lang.reflect.*;

public class Main_01 {

	public static void main(String[] args) {

		Example_01 example = new Example_01("10", "20", "30");
		Class<? extends Example_01> exampleC = example.getClass();

		Constructor[] declaredConstructors = exampleC.getDeclaredConstructors();
		for (int i = 0; i < declaredConstructors.length; i++) {
			Constructor<?> constructor = declaredConstructors[i];
			System.out.println("查看是否允許帶有可變數量的參數：" + constructor.isVarArgs());
			System.out.println("該構造方法的入口參數類型依次爲：");
			Class[] parameterTypes = constructor.getParameterTypes();
			for (int j = 0; j < parameterTypes.length; j++) {
				System.out.println(" " + parameterTypes[j]);
			}
			System.out.println("該構造方法可能拋出的異常類型爲：");
			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) {
					System.out.println("在創建對象時拋出異常，下面執行setAccessible()方法");
					constructor.setAccessible(true);
				}
			}
			if(example2!=null){
			example2.print();
			System.out.println();
			}
		}

	}

}