Programming Language►Java

[Java] Shallow Copy和Deep Copy

前言

在複製陣列的時候，要注意是需要Shallow Copy還是Deep Copy，直接看程式碼。

Shallow Copy

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import java.util.*;
import java.io.*;
class Test
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int a[] = {1,2,3,4,5} ;
		int b[] = a ;
		
		System.out.print("a = ");
		for ( int i = 0 ; i < a.length ; i ++ )
			System.out.print(a[i]+" ") ;
		System.out.println();
		System.out.print("b = ");
		for ( int i = 0 ; i < a.length ; i ++ )
			System.out.print(b[i]+" ") ;
		System.out.println();
		
		a[1] = 7 ;
		
		System.out.print("a = ");
		for ( int i = 0 ; i < a.length ; i ++ )
			System.out.print(a[i]+" ") ;
		System.out.println();
		System.out.print("b = ");
		for ( int i = 0 ; i < a.length ; i ++ )
			System.out.print(b[i]+" ") ;
		System.out.println();
		
	}
}

可以看到當a改變的時候b也跟著改變了，這是因為b是reference到a陣列，但如果要個別獨立就必須使用Deep Copy。

Deep Copy

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import java.util.*;
import java.io.*;
class Test
{
	public static void main (String[] args) throws java.lang.Exception
	{
		int a[] = {1,2,3,4,5} ;
		int b[] = new int[a.length] ;
		
		for ( int i = 0 ; i < a.length ; i ++ )
			b[i] = a[i] ;
		
		System.out.print("a = ");
		for ( int i = 0 ; i < a.length ; i ++ )
			System.out.print(a[i]+" ") ;
		System.out.println();
		System.out.print("b = ");
		for ( int i = 0 ; i < a.length ; i ++ )
			System.out.print(b[i]+" ") ;
		System.out.println();
		
		a[1] = 7 ;
		
		System.out.print("a = ");
		for ( int i = 0 ; i < a.length ; i ++ )
			System.out.print(a[i]+" ") ;
		System.out.println();
		System.out.print("b = ");
		for ( int i = 0 ; i < a.length ; i ++ )
			System.out.print(b[i]+" ") ;
		System.out.println();
		
	}
}

簡單來說就是先配置記憶體位置給b，再將a的內容逐項複製過去。