This is an example of how to make a generic copy of a class, using Java reflection. In order to make a generic copy of a class we have created two classes and then copied the one to the other, as described below:
- We have created two classes
AandB.Bclass has a String and an int field and overrides thetoString()method inherited from Object.Aclass has two int fields, and aBfield and also overrides thetoString()method inherited from Object. - We have also created a class,
GenericCopy, that consists of a method,static >T< void copyFields(T from, T to). The method reads each Field from a source class, usinggetClass(),getFields()API methods of Class, and for each one of them checks if its type isPrimitive, using theboolean isPrimitivish(Class c)method ofGenericCopy. - In
boolean isPrimitivish(Class c)method the type of each field is checked and returned. ThegetType()API method of Field is used to get the type of each field. If a field has a primitive type or its type is equal to one of the classes that wrap the values of the primitive types, then this field in the target class is replaced with the value of the same field from the source class. Else, thecopyFields(T from, T to)method is called for the specified field.
Let’s take a look at the code snippet that follows:
001 002 003 004 005 006 007 008 009 010 011 012 013 014 015 016 017 018 019 020 021 022 023 024 025 026 027 028 029 030 031 032 033 034 035 036 037 038 039 040 041 042 043 044 045 046 047 048 049 050 051 052 053 054 055 056 057 058 059 060 061 062 063 064 065 066 067 068 069 070 071 072 073 074 075 076 077 078 079 080 081 082 083 084 085 086 087 088 089 090 091 092 093 094 095 096 097 098 099 100 101 102 103 104 105 106 107 108 109 110 111 112 113 114 115 116 117 118 119 120 121 122 123 124 125 126 127 128 129 130 131 132 133 134 | package com.javacodegeeks.snippets.core;import java.lang.reflect.Field;public class GenericCopy { /** * Deep-copies the values from one object to the other * */ public static void main(String[] args) { A a1 = new A(1, 2, new B("string 1", 10)); A a2 = new A(3, 4, new B("string 2", 20)); System.out.println("a1 is :" + a1); System.out.println("a2 is :" + a2); copyFields(a1, a2); System.out.println("After copying..."); System.out.println("a1 is :" + a1); System.out.println("a2 is :" + a2); } public static <T> void copyFields(T from, T to) { for (Field f : from.getClass().getFields()) {try { if (isPrimitivish(f.getType())) { f.set(to, f.get(from)); } else { copyFields(f.get(from), f.get(to)); }} catch (IllegalArgumentException | IllegalAccessException e) { e.printStackTrace();} } } private static boolean isPrimitivish(Class c) { return c.isPrimitive() || c == String.class || c == Boolean.class || c == Byte.class || c == Short.class || c == Character.class || c == Integer.class || c == Float.class || c == Double.class || c == Long.class; }}class A { public int x; public int y; public B bObj; public A(int x, int y, B b) { this.x = x; this.y = y; this.bObj = b; } @Override public String toString() { return "[" + this.x + "," + this.y + "," + this.bObj.toString() + "]"; }}class B { public String str; public int z; public B(String str, int z) { this.str = str; this.z = z; } @Override public String toString() { return "[" + this.str + "," + this.z + "]"; }} |
Output:
a1 is :[1,2,[string 1,10]]
a2 is :[3,4,[string 2,20]]
After copying...
a1 is :[1,2,[string 1,10]]
a2 is :[1,2,[string 1,10]]
This was an example of how to make a generic copy of a class in Java.
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