java 自学日志【十九】---基础加强DAY26下

class Demo
{
public static void main(String[] args)
{
String str = "abc";
Class cls1 = str.getClass();
Class cls2 = String.class;
Class cls3 = Class.forName("java.lang.String");

System.out.println(cls1 == cls2);
System.out.println(cls1 == cls3);

System.out.println(cls1.isPrimitive());
System.out.println(int.class.isPrimitive());
System.out.println(Integer.class.isPrimitive());
System.out.println(Integer.TYPE.isPrimitive());
System.out.println(int[].class.isArray());
}
}

public class ReflectPoint
{
private int x；
public  int y；
public String str1 = "Master";
public String str2 = "Basketball";
public String str3 = "itcast";

public ReflectPoint(int x ,int y)
{
super();
this.x=x;
this.y = y;
}
}

class Demo
{
private static void changeStringValue(Object obj) throws Exception
{
Field [] fields = obj.getClass().getFields();
for(Field field:fields)
{
if(field.getType()==String.class)
{	//字节码的比较用==更精确，因为比较的字节码是同一份文件；
String str =(String) field.get(obj);
String str1 = str.replace('a','w');
field.set(obj, str1);
}
}
}
public static void main(String[] args)
{
changeStringValue(ref);
System.out.println(ref);
}
}

class TestArguments
{
public static void main(String [] args)
{
for(String arg:args)
{
System.out.println(arg);
}
}
}

String startingClassName =args[0];//注意，要在该程序的运行环境中配置args为TestArguments;

Method mainMethod =Class.forName(startingClassName).getMethod("main",String[].class);
//new Object[]{new String[]{"ball","wife"}

mainMethod.invoke(null,new Object[]{new String[]{"ball","wife"}});
//这句为什么？JDK1.5向下兼容1.4版本，而1.4版本中，会把传递进的数组当一个个参数的组成的数组，而进行拆分。这句调用的是1.4的方法。

mainMethod.invoke(null,(Object)new String[]{"ball","wife"});//这句是调用了1.5的方法。

int[] a1 =new  int [3];
int[] a2 = new int [4];
int[][] a3 = new int[2][3];
String[] a4 = new String[]{"111","222","333"};
Class cl1 =a1.getClass();

System.out.println(a1.getClass() == a2.getClass());//true;
//      System.out.println(a1.getClass() == a3.getClass());//MyEclipse会报错
//      System.out.println(a1.getClass() == a4.getClass());//MyEclipse会报错
System.out.println("a1:"+a1.getClass().getName());
System.out.println("a2:"+a2.getClass().getName());
System.out.println("a3:"+a3.getClass().getName());
System.out.println("a4:"+a4.getClass().getName());
System.out.println(a1.getClass().getSuperclass().getName());
System.out.println(a4.getClass().getSuperclass().getName());

// Object[] obj1 = a1;//这句是错误的
Object obj2 = a2;
Object[] obj3 = a3;
Object[] obj4 = a4;
//Arrays工具类，可以把数组当成集合来打印，但如果数组元素的类型是基本数据类型，那么打印的是数组引用的地址，而不是每个元素的值
System.out.println(Arrays.asList(a1));
System.out.println(Arrays.asList(a4));

class Demo
{
private static void printObject(Object obj)
{
Class cla = obj.getClass();
if(cla.isArray())
{
int len = Array.getLength(obj);
for(int x=0;x<len;x++)
{
System.out.println(Array.get(obj, x));
}

}
else
{
System.out.println(obj);
}
}
public static void main(String[] args)
{
printObject(a4);
printObject("zyx");
}
}

Collection collection= new ArrayList();//new HashSet();
ReflectPoint p1 = new ReflectPoint(4,4);
ReflectPoint p2 = new ReflectPoint(2,5);
ReflectPoint p3 = new ReflectPoint(7,6);
ReflectPoint p4 = new ReflectPoint(4,4);

collection.add(p1);
collection.add(p2);
collection.add(p3);
collection.add(p1);
//重写ReflectPoint的hashCode和equals方法，让x和y参与其重新方法内。
/*
@Override
public int hashCode() {
final int prime = 31;
int result = 1;
result = prime * result + x;
result = prime * result + y;
return result;
}
@Override//如果把这句去掉，下边写成equals(ReflectPoint obj)不会报错
public boolean equals(Object obj) {//Object不能改成ReflectPoint，否则就不是重写，而是重载了
if (this == obj)
return true;
if (obj == null)
return false;
if (getClass() != obj.getClass())
return false;
ReflectPoint other = (ReflectPoint) obj;
if (x != other.x)
return false;
if (y != other.y)
return false;
return true;
}
*/
System.out.println(collection.size())//ArrayList值为4，HashSet则值为3;
p1.y= 8;//HashSet集合中，p1元素的y参与了hashcode值的运算，所以改变y后，导致无法删除和重复加入该元素。
System.out.println(collection.remove(p1));//ArrayList的remove 方法，删除列表中第一次出现的p1
System.out.println(collection.size());//ArrayListz值减少一个为3，HashSet无法删除，所以值不变仍为3;

InputStream ips = ReflectTest2.class.getResourceAsStream("config.properties");
Properties prop = new Properties();
prop.load(ips);
ips.close();
String className = prop.getProperty("className");
Collection collection = (Collection) Class.forName(className).newInstance()
//注意：用newInstance时，必须该类有空参构造方法，否则会出现初始化异常;
ReflectPoint p1 = new ReflectPoint(4,4);
ReflectPoint p2 = new ReflectPoint(2,5);
ReflectPoint p3 = new ReflectPoint(7,6);
ReflectPoint p4 = new ReflectPoint(4,4);

collection.add(p1);
collection.add(p2);
collection.add(p3);
collection.add(p1);

System.out.println(collection.size())//配置文件中className为ArrayList时，值为4，为HashSet时值为3;