Java by API/java.lang.reflect/Constructor

Constructor: getExceptionTypes()

  
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Member;
import java.lang.reflect.Method;
import java.lang.reflect.Modifier;
public class Main{
  public static void main(String[] args) throws ClassNotFoundException {
    Class c = Class.forName(args[0]);
    print_class(c);
  }
  public static void print_class(Class c) {
    if (c.isInterface()) {
      System.out.print(Modifier.toString(c.getModifiers()) + " " + typename(c));
    } else if (c.getSuperclass() != null) {
      System.out.print(Modifier.toString(c.getModifiers()) + " class " + typename(c) + " extends "
          + typename(c.getSuperclass()));
    } else {
      System.out.print(Modifier.toString(c.getModifiers()) + " class " + typename(c));
    }
    Class[] interfaces = c.getInterfaces();
    if ((interfaces != null) && (interfaces.length > 0)) {
      if (c.isInterface())
        System.out.print(" extends ");
      else
        System.out.print(" implements ");
      for (int i = 0; i < interfaces.length; i++) {
        if (i > 0)
          System.out.print(", ");
        System.out.print(typename(interfaces[i]));
      }
    }
    System.out.println(" {"); 
    Constructor[] constructors = c.getDeclaredConstructors();
    for (int i = 0; i < constructors.length; i++)
      print_method_or_constructor(constructors[i]);
    Field[] fields = c.getDeclaredFields();
    for (int i = 0; i < fields.length; i++){
      print_field(fields[i]);
    }
    Method[] methods = c.getDeclaredMethods();
    for (int i = 0; i < methods.length; i++)
      print_method_or_constructor(methods[i]);
    System.out.println("}");
  }
  public static String typename(Class t) {
    String brackets = "";
    while (t.isArray()) {
      brackets += "[]";
      t = t.getComponentType();
    }
    String name = t.getName();
    int pos = name.lastIndexOf(".");
    if (pos != -1)
      name = name.substring(pos + 1);
    return name + brackets;
  }
  public static String modifiers(int m) {
    if (m == 0)
      return "";
    else
      return Modifier.toString(m) + " ";
  }
  public static void print_field(Field f) {
    System.out.println("  " + modifiers(f.getModifiers()) + typename(f.getType()) + " "
        + f.getName() + ";");
  }
  public static void print_method_or_constructor(Member member) {
    Class returntype = null, parameters[], exceptions[];
    if (member instanceof Method) {
      Method m = (Method) member;
      returntype = m.getReturnType();
      parameters = m.getParameterTypes();
      exceptions = m.getExceptionTypes();
      System.out.print("  " + modifiers(member.getModifiers()) + typename(returntype) + " "
          + member.getName() + "(");
    } else {
      Constructor c = (Constructor) member;
      parameters = c.getParameterTypes();
      exceptions = c.getExceptionTypes();
      System.out.print("  " + modifiers(member.getModifiers()) + typename(c.getDeclaringClass())
          + "(");
    }
    for (int i = 0; i < parameters.length; i++) {
      if (i > 0)
        System.out.print(", ");
      System.out.print(typename(parameters[i]));
    }
    System.out.print(")");
    if (exceptions.length > 0)
      System.out.print(" throws ");
    for (int i = 0; i < exceptions.length; i++) {
      if (i > 0)
        System.out.print(", ");
      System.out.print(typename(exceptions[i]));
    }
    System.out.println(";");
  }
}

Constructor: getModifiers()

  
import static java.lang.System.out;
import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
public class Main {
  public static void main(String... args) throws Exception {
    Class<?> c = Class.forName(args[0]);
    Constructor[] allConstructors = c.getDeclaredConstructors();
    for (Constructor ctor : allConstructors) {
      int searchMod = modifierFromString(args[1]);
      int mods = accessModifiers(ctor.getModifiers());
      if (searchMod == mods) {
        out.format("%s%n", ctor.toGenericString());
        out.format("  [ synthetic=%-5b var_args=%-5b ]%n", ctor.isSynthetic(), ctor.isVarArgs());
      }
    }
  }
  private static int accessModifiers(int m) {
    return m & (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED);
  }
  private static int modifierFromString(String s) {
    if ("public".equals(s))
      return Modifier.PUBLIC;
    else if ("protected".equals(s))
      return Modifier.PROTECTED;
    else if ("private".equals(s))
      return Modifier.PRIVATE;
    else if ("package-private".equals(s))
      return 0;
    else
      return -1;
  }
}

Constructor: getName()

  
/*
java.util.ArrayList: 
java.util.ArrayList: Collection 
java.util.ArrayList: int 
 
 */
import java.lang.reflect.Constructor;
public class MainClass {
  public static void main(String[] args) {
    try {
      Class c = Class.forName("java.util.ArrayList");
      Constructor constructors[] = c.getConstructors();
      for (int i = 0; i < constructors.length; i++) {
        System.out.print(constructors[i].getName() + ": ");
        Class parameters[];
        parameters = constructors[i].getParameterTypes();
        for (int j = 0; j < parameters.length; j++) {
          String s = parameters[j].getName();
          s = s.substring(s.lastIndexOf(".") + 1, s.length());
          System.out.print(s + " ");
        }
        System.out.println("");
      }
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }
}

Constructor: getParameterTypes()

  
/*
java.util.ArrayList: 
java.util.ArrayList: Collection 
java.util.ArrayList: int 
 
 */
import java.lang.reflect.Constructor;
public class MainClass {
  public static void main(String[] args) {
    try {
      Class c = Class.forName("java.util.ArrayList");
      Constructor constructors[] = c.getConstructors();
      for (int i = 0; i < constructors.length; i++) {
        System.out.print(constructors[i].getName() + ": ");
        Class parameters[];
        parameters = constructors[i].getParameterTypes();
        for (int j = 0; j < parameters.length; j++) {
          String s = parameters[j].getName();
          s = s.substring(s.lastIndexOf(".") + 1, s.length());
          System.out.print(s + " ");
        }
        System.out.println("");
      }
    } catch (Exception ex) {
      ex.printStackTrace();
    }
  }
}

Constructor: newInstance(Object... initargs)

  

import java.lang.reflect.Constructor;
public class Main {
  public static void main(final String[] args) throws Exception {
    final Class[] ARG_TYPES = new Class[] { String.class };
    Constructor cst = Integer.class.getConstructor(ARG_TYPES);
    System.out.println(cst.newInstance(new Object[] { "45" }));
  }
}

Constructor: setAccessible(boolean flag)

 

import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.Method;
public class Main {
  public static void main(String[] argv) throws Exception {
    Class cls = java.lang.String.class;
    Method method = cls.getMethods()[0];
    Field field = cls.getFields()[0];
    Constructor constructor = cls.getConstructors()[0];
    field.setAccessible(true);
    constructor.setAccessible(true);
    method.setAccessible(true);
  }
}

Constructor: toGenericString()

  
import static java.lang.System.out;
import java.lang.reflect.Constructor;
import java.lang.reflect.Modifier;
public class Main {
  public static void main(String... args) throws Exception {
    Class<?> c = Class.forName(args[0]);
    Constructor[] allConstructors = c.getDeclaredConstructors();
    for (Constructor ctor : allConstructors) {
      int searchMod = modifierFromString(args[1]);
      int mods = accessModifiers(ctor.getModifiers());
      if (searchMod == mods) {
        out.format("%s%n", ctor.toGenericString());
        out.format("  [ synthetic=%-5b var_args=%-5b ]%n", ctor.isSynthetic(), ctor.isVarArgs());
      }
    }
  }
  private static int accessModifiers(int m) {
    return m & (Modifier.PUBLIC | Modifier.PRIVATE | Modifier.PROTECTED);
  }
  private static int modifierFromString(String s) {
    if ("public".equals(s))
      return Modifier.PUBLIC;
    else if ("protected".equals(s))
      return Modifier.PROTECTED;
    else if ("private".equals(s))
      return Modifier.PRIVATE;
    else if ("package-private".equals(s))
      return 0;
    else
      return -1;
  }
}