Java學習筆記-12.傳遞和返回對象

1.Clone()方法產生一個object，使用方法後必須產生的object賦值。

Vector v2 = (Vector)v.clone();

2.Clone()方法在object中是保護類型方法，如果自己創建的類需要使用Clone()方法的話需要自己重新寫一個，並且繼承Cloneable介面。

package tweleve;

import java.util.*;

class MyObject implements Cloneable {
    int i;

    MyObject(int ii) {
        i = ii;
    }

    public Object clone() {
        Object object = null;
        try {
            object = super.clone();
        } catch (CloneNotSupportedException e) {
            System.out.println("MyObject can't clone");
        }
        return object;
    }

    public String toString() {
        return Integer.toString(i);
    }
}

public class LocalCopy {
    static MyObject g(MyObject v) {
        v.i++;
        return v;
    }

    static MyObject f(MyObject v) {
        v = (MyObject) v.clone();
        v.i++;
        return v;
    }

    public static void main(String[] args) {
        MyObject aMyObject = new MyObject(11);
        MyObject bMyObject = g(aMyObject);
        if (aMyObject == bMyObject)
            System.out.println("a==b");
        else
            System.out.println("a!=b");
        System.out.println("a=" + aMyObject);
        System.out.println("b=" + bMyObject);
        MyObject cMyObject = new MyObject(31);
        MyObject dMyObject = f(cMyObject);
        if (cMyObject == dMyObject)
            System.out.println("c==d");
        else
            System.out.println("c!=d");
        System.out.println("c=" + cMyObject);
        System.out.println("d=" + dMyObject);

    }

}

3.如果希望一個類能夠克隆那麼需要有下列步驟：(1)實現Cloneable介面

                                                                             (2)覆蓋Clone()方法

                                                                             (3)在自己的Clone()方法中調用super.clone()

                                                                             (4)在自己的clone()中捕獲違例 

4.String類中所有能修改String的方法其實都創建和返回了一個新的String類，原來的String類是沒有改變的，包括+和+=，StringBuffer比String操作字元串時更有效。

package tweleve;

import java.sql.Ref;

import org.omg.CORBA.SystemException;

public class Stringer {
    static String upcase(String s){
         return s.toUpperCase();
    }
    
    public static void main(String[] args){
        String qString=new String("howdy");
        System.out.println(qString);
        String qq=upcase(qString);
        System.out.println(qq);
        System.out.println(qString);
    }

}