I'm trying to clone an instance of a custom class I made called CSP. I have one instance called csp and I want to make a clone of csp called cspclone. Here is what I'm using to do that:
CSP cspclone = new CSP((csp.x).clone(), (csp.d).clone(), (csp.c).clone());
For some reason though when I pass cspclone to a method that modifies it csp gets modified also as if I forgot the .clone() functions but I didn't! Why is this happening?!
Override the clone method in CSP:
public class CSP {
private String aField;
private int[] array;
private int[][] twoDArr;
private List<ALContent> list; //here ALContent also needs to override clone properly
@Override
public Object clone() {
CSP clone = new CSP();
clone.aField = this.aField;
clone.array = new int[this.array.length];
System.arraycopy(this.array, 0, clone.array, 0, this.array.length);
clone.list = new ArrayList<ALContent>();
for(ALContent content : this.list) {
clone.list.add(content.clone()); //make sure you add the clone of the content
}
clone.twoDArr = new int[this.twoDArr.length][];
for(int i=0; i<this.twoDArr.length; i++) {
clone.twoDArr[i] = new int[this.twoDArr[i].length];
System.arraycopy(this.twoDArr[i], 0, clone.twoDArr[i], 0, this.twoDArr[i].length);
}
return clone;
}
}
Then you can do:
CSP csp = new CSP();
CSP cspClone = (CSP) csp.clone();
//... is?public int[] x; public ArrayList<String> d[]; public int[][] c;
clone in ArrayList does shallow copy: download.oracle.com/javase/6/docs/api/java/util/…. So, you have to do it manully: stackoverflow.com/questions/715650/….If your properties of array type use System.arraycopy
According to http://download.oracle.com/javase/1.3/docs/api/java/lang/Object.html#clone%28%29
this method creates a new instance of the class of this object and initializes all its fields with exactly the contents of the corresponding fields of this object, as if by assignment; the contents of the fields are not themselves cloned. Thus, this method performs a "shallow copy" of this object, not a "deep copy" operation.
You might have to override the clone method and clone() a reference type attribute within the object (i.e., perform deep copy operation).
To solve your problem you need deep cloning. The default clone method does a shallow copy. See Object.clone().
Here are some approaches. All have advantages and drawbacks.
Here are several other stackoverflow discussions of cloning.
.clone()only performs a shallow copy of your object, so references to the fields in csp are being copied into cspclone.