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Java - conversion from string to generic type

In C #, I could do something like this

public static TConvertible ChangeType<TConvertible>(object value) where TConvertible : IConvertible { try { if (value == null) return default(TConvertible); return (TConvertible)Convert.ChangeType(value, typeof(TConvertible)); } catch (System.FormatException) { return default(TConvertible); } }

Is there a way to do something like this in java? I am using android SharedPreferences and trying to wrap a control class around it. Instead of using getString , getInt , getLong , etc. I would like to pass the value, save it as a string and then convert back to it.

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2 answers

I believe this is not possible due to the implementation of Java generic generators and the problem of erasing all types, since he would not know that TConvertible is at run time.

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try my new class

  /* * To change this template, choose Tools | Templates * and open the template in the editor. */ package sk.freeit.utils; import java.lang.reflect.Constructor; import java.lang.reflect.InvocationTargetException; import java.lang.reflect.Method; /** * * @author radenko * radovan.kadlic@gmail.com */ public class Convert { protected static Object invokeMethod(Object obj, String valMethod) throws NoSuchMethodException, IllegalAccessException, IllegalArgumentException, InvocationTargetException { Method intValue = obj.getClass().getMethod(valMethod); return intValue.invoke(obj); } protected static Object makeNew(Class type, Object obj) throws NoSuchMethodException, InstantiationException, IllegalAccessException, IllegalArgumentException, InvocationTargetException { Constructor constructor = type.getConstructor(obj.getClass()); return constructor.newInstance(obj); } public static boolean booleanValue(String str) { str = str.toLowerCase(); return !str.isEmpty() && !str.equals("0") && !str.equals("no") && !str.equals("n") && !str.equals("false"); } public static boolean booleanValue(Object obj) { Class srcType = obj.getClass(); if (srcType.equals(boolean.class)||srcType.equals(Boolean.class)) return (Boolean)obj; else if (srcType.equals(byte.class) || srcType.equals(Byte.class)) return ((Byte)obj)!=0; else if (srcType.equals(char.class) || srcType.equals(Character.class)) return ((Character)obj)!='\0'; else if (srcType.equals(double.class) || srcType.equals(Double.class)) return ((Double)obj)!=0.0; else if (srcType.equals(float.class) || srcType.equals(Float.class)) return ((Float)obj)!=0.0; else if (srcType.equals(int.class) || srcType.equals(Integer.class)) return ((Integer)obj)!=0.0; else if (srcType.equals(long.class) || srcType.equals(Long.class)) return ((Long)obj)!=0L; else if (srcType.equals(short.class) || srcType.equals(Short.class)) return ((Short)obj)!=0; else if(srcType.equals(String.class)) return booleanValue(obj.toString()); else { try { return (Boolean)invokeMethod(obj, "booleanValue"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return booleanValue(obj.toString()); } public static byte byteValue(Object obj) { Class srcType = obj.getClass(); if (srcType.equals(boolean.class)||srcType.equals(Boolean.class)) return ((Boolean)obj)?(byte)1:(byte)0; else if (srcType.equals(byte.class) || srcType.equals(Byte.class)) return ((Byte)obj); else if (srcType.equals(char.class) || srcType.equals(Character.class)) return (byte)Character.getNumericValue((Character)obj); else if (srcType.equals(double.class) || srcType.equals(Double.class)) return ((Double)obj).byteValue(); else if (srcType.equals(float.class) || srcType.equals(Float.class)) return ((Float)obj).byteValue(); else if (srcType.equals(int.class) || srcType.equals(Integer.class)) return ((Integer)obj).byteValue(); else if (srcType.equals(long.class) || srcType.equals(Long.class)) return ((Long)obj).byteValue(); else if (srcType.equals(short.class) || srcType.equals(Short.class)) return ((Short)obj).byteValue(); else if(srcType.equals(String.class)) return Byte.parseByte((String)obj); else { try { return (Byte)invokeMethod(obj,"byteValue"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return Byte.parseByte(obj.toString()); } public static char charValue(Object obj) { Class srcType = obj.getClass(); if (srcType.equals(boolean.class)||srcType.equals(Boolean.class)) return ((Boolean)obj)?'\0':'Y'; else if (srcType.equals(byte.class) || srcType.equals(Byte.class)) return Character.forDigit((Byte)obj,10); else if (srcType.equals(char.class) || srcType.equals(Character.class)) return (Character)obj; else if (srcType.equals(double.class) || srcType.equals(Double.class)) return Character.forDigit(((Double)obj).intValue(),10); else if (srcType.equals(float.class) || srcType.equals(Float.class)) return Character.forDigit(((Float)obj).intValue(),10); else if (srcType.equals(int.class) || srcType.equals(Integer.class)) return Character.forDigit((Integer)obj,10); else if (srcType.equals(long.class) || srcType.equals(Long.class)) return Character.forDigit(((Long)obj).intValue(),10); else if (srcType.equals(short.class) || srcType.equals(Short.class)) return Character.forDigit((Short)obj,10); else if(srcType.equals(String.class)) return ((String)obj).charAt(0); else { try { return (Character)invokeMethod(obj, "charValue"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return obj.toString().charAt(0); } public static double doubleValue(Object obj) { Class srcType = obj.getClass(); if (srcType.equals(boolean.class)||srcType.equals(Boolean.class)) return ((Boolean)obj)?1.0:0.0; else if (srcType.equals(byte.class) || srcType.equals(Byte.class)) return ((Byte)obj).doubleValue(); else if (srcType.equals(char.class) || srcType.equals(Character.class)) return Character.getNumericValue((Character)obj); else if (srcType.equals(double.class) || srcType.equals(Double.class)) return ((Double)obj).doubleValue(); else if (srcType.equals(float.class) || srcType.equals(Float.class)) return ((Float)obj).doubleValue(); else if (srcType.equals(int.class) || srcType.equals(Integer.class)) return ((Integer)obj).doubleValue(); else if (srcType.equals(long.class) || srcType.equals(Long.class)) return ((Long)obj).doubleValue(); else if (srcType.equals(short.class) || srcType.equals(Short.class)) return ((Short)obj).doubleValue(); else if(srcType.equals(String.class)) return Double.parseDouble((String)obj); else { try { return (Double)invokeMethod(obj, "doubleValue"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return Double.parseDouble(obj.toString()); } public static float floatValue(Object obj) { Class srcType = obj.getClass(); if (srcType.equals(boolean.class)||srcType.equals(Boolean.class)) return ((Boolean)obj)?1.0f:0.0f; else if (srcType.equals(byte.class) || srcType.equals(Byte.class)) return ((Byte)obj); else if (srcType.equals(char.class) || srcType.equals(Character.class)) return Character.getNumericValue((Character)obj); else if (srcType.equals(double.class) || srcType.equals(Double.class)) return ((Double)obj).floatValue(); else if (srcType.equals(float.class) || srcType.equals(Float.class)) return ((Float)obj); else if (srcType.equals(int.class) || srcType.equals(Integer.class)) return ((Integer)obj).floatValue(); else if (srcType.equals(long.class) || srcType.equals(Long.class)) return ((Long)obj); else if (srcType.equals(short.class) || srcType.equals(Short.class)) return ((Short)obj); else if(srcType.equals(String.class)) return Float.parseFloat((String)obj); else { try { return (Float)invokeMethod(obj, "floatValue"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return Float.parseFloat(obj.toString()); } public static int intValue(Object obj) { Class srcType = obj.getClass(); if (srcType.equals(boolean.class)||srcType.equals(Boolean.class)) return ((Boolean)obj)?1:0; else if (srcType.equals(byte.class) || srcType.equals(Byte.class)) return ((Byte)obj).intValue(); else if (srcType.equals(char.class) || srcType.equals(Character.class)) { return Character.getNumericValue((Character)obj); } else if (srcType.equals(double.class) || srcType.equals(Double.class)) return ((Double)obj).intValue(); else if (srcType.equals(float.class) || srcType.equals(Float.class)) return ((Float)obj).intValue(); else if (srcType.equals(int.class) || srcType.equals(Integer.class)) return ((Integer)obj).intValue(); else if (srcType.equals(long.class) || srcType.equals(Long.class)) return ((Long)obj).intValue(); else if (srcType.equals(short.class) || srcType.equals(Short.class)) return ((Short)obj).intValue(); else if(srcType.equals(String.class)) return Integer.parseInt((String)obj); else { try { return (Integer)invokeMethod(obj, "intValue"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return Integer.parseInt(obj.toString()); } public static long longValue(Object obj) { Class srcType = obj.getClass(); if (srcType.equals(boolean.class)||srcType.equals(Boolean.class)) return ((Boolean)obj)?1:0; else if (srcType.equals(byte.class) || srcType.equals(Byte.class)) return ((Byte)obj); else if (srcType.equals(char.class) || srcType.equals(Character.class)) return Character.getNumericValue((Character)obj); else if (srcType.equals(double.class) || srcType.equals(Double.class)) return ((Double)obj).longValue(); else if (srcType.equals(float.class) || srcType.equals(Float.class)) return ((Float)obj).longValue(); else if (srcType.equals(int.class) || srcType.equals(Integer.class)) return ((Integer)obj); else if (srcType.equals(long.class) || srcType.equals(Long.class)) return ((Long)obj); else if (srcType.equals(short.class) || srcType.equals(Short.class)) return ((Short)obj); else if(srcType.equals(String.class)) return Long.parseLong((String)obj); else { try { return (Long)invokeMethod(obj, "longValue"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return Long.parseLong(obj.toString()); } public static short shortValue(Object obj) { Class srcType = obj.getClass(); if (srcType.equals(boolean.class)||srcType.equals(Boolean.class)) return ((Boolean)obj)?(short)1:(short)0; else if (srcType.equals(byte.class) || srcType.equals(Byte.class)) return ((Byte)obj).shortValue(); else if (srcType.equals(char.class) || srcType.equals(Character.class)) return (short)Character.getNumericValue((Character)obj); else if (srcType.equals(double.class) || srcType.equals(Double.class)) return ((Double)obj).shortValue(); else if (srcType.equals(float.class) || srcType.equals(Float.class)) return ((Float)obj).shortValue(); else if (srcType.equals(int.class) || srcType.equals(Integer.class)) return ((Integer)obj).shortValue(); else if (srcType.equals(long.class) || srcType.equals(Long.class)) return ((Long)obj).shortValue(); else if (srcType.equals(short.class) || srcType.equals(Short.class)) return ((Short)obj); else if(srcType.equals(String.class)) return Short.parseShort((String)obj); else { try { return (Short)invokeMethod(obj, "shortValue"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return Short.parseShort(obj.toString()); } public static Object changeType (Object obj, Class type) { if (obj.getClass().equals(type)) return obj; if (type.equals(boolean.class)||type.equals(Boolean.class)) return booleanValue(obj); else if (type.equals(byte.class) || type.equals(Byte.class)) return byteValue(obj); else if (type.equals(char.class) || type.equals(Character.class)) return charValue(obj); else if (type.equals(double.class) || type.equals(Double.class)) return doubleValue(obj); else if (type.equals(float.class) || type.equals(Float.class)) return floatValue(obj); else if (type.equals(int.class) || type.equals(Integer.class)) return intValue(obj); else if (type.equals(long.class) || type.equals(Long.class)) return longValue(obj); else if (type.equals(short.class) || type.equals(Short.class)) return shortValue(obj); else if(type.equals(String.class)) return obj.toString(); else { try { invokeMethod(obj,type.getName()+"Value"); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } try { invokeMethod(obj,"to"+type.getName()); } catch (NoSuchMethodException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } try { return makeNew(type, obj); } catch (NoSuchMethodException ex) { } catch (InstantiationException ex) { } catch (IllegalAccessException ex) { } catch (IllegalArgumentException ex) { } catch (InvocationTargetException ex) { } } return type.cast(obj); } }

Radenko

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Source: https://habr.com/ru/post/1340346/

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