Array Copy in Java

Array in Java can be copied to another array using the following ways.

• Using variable assignment. This method has side effects as changes to the element of an array reflects on both the places. To prevent this side effect following are the better ways to copy the array elements.

• Create a new array of the same length and copy each element.

• Use the clone method of the array. Clone methods create a new array of the same size.

• Use System.arraycopy() method.  The arraycopy() can be used to copy a subset of an array.

Example

Create a java class named Tester.

Tester.java

<span class="kwd">public</span><span class="pln"> </span><span class="kwd">class</span><span class="pln"> </span><span class="typ">Tester</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
   </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> main</span><span class="pun">(</span><span class="typ">String</span><span class="pln"> args</span><span class="pun">[])</span><span class="pln"> </span><span class="pun">{</span><span class="pln">      
      </span><span class="com">//Scenario 1: Copy array using assignment</span><span class="pln">
      </span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> a </span><span class="pun">=</span><span class="pln"> </span><span class="pun">{</span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">2</span><span class="pun">,</span><span class="pln"> </span><span class="lit">3</span><span class="pun">};</span><span class="pln">      
      </span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> b </span><span class="pun">=</span><span class="pln"> a</span><span class="pun">;</span><span class="pln">

      </span><span class="com">//test side effect</span><span class="pln">
      b</span><span class="pun">[</span><span class="lit">0</span><span class="pun">]++;</span><span class="pln">

      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Scenario 1: "</span><span class="pun">);</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Array a: "</span><span class="pun">);</span><span class="pln">
      printArray</span><span class="pun">(</span><span class="pln">a</span><span class="pun">);</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Array b: "</span><span class="pun">);</span><span class="pln">
      printArray</span><span class="pun">(</span><span class="pln">b</span><span class="pun">);</span><span class="pln">

      </span><span class="com">//Scenario 2: Copy array by iterating</span><span class="pln">
      </span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> c </span><span class="pun">=</span><span class="pln"> </span><span class="pun">{</span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">2</span><span class="pun">,</span><span class="pln"> </span><span class="lit">3</span><span class="pun">};</span><span class="pln">       </span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> d </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="kwd">int</span><span class="pun">[</span><span class="pln">c</span><span class="pun">.</span><span class="pln">length</span><span class="pun">];</span><span class="pln">
      </span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln"> i </span><span class="pun"><</span><span class="pln"> d</span><span class="pun">.</span><span class="pln">length</span><span class="pun">;</span><span class="pln"> i</span><span class="pun">++)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
         d</span><span class="pun">[</span><span class="pln">i</span><span class="pun">]</span><span class="pln"> </span><span class="pun">=</span><span class="pln"> c</span><span class="pun">[</span><span class="pln">i</span><span class="pun">];</span><span class="pln">
      </span><span class="pun">}</span><span class="pln">

      </span><span class="com">//test side effect</span><span class="pln">
      d</span><span class="pun">[</span><span class="lit">0</span><span class="pun">]++;</span><span class="pln">

      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Scenario 2: "</span><span class="pun">);</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Array c: "</span><span class="pun">);</span><span class="pln">
      printArray</span><span class="pun">(</span><span class="pln">c</span><span class="pun">);</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Array d: "</span><span class="pun">);</span><span class="pln">
      printArray</span><span class="pun">(</span><span class="pln">d</span><span class="pun">);</span><span class="pln">

      </span><span class="com">//Scenario 3: Copy array using clone</span><span class="pln">
      </span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> e </span><span class="pun">=</span><span class="pln"> </span><span class="pun">{</span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">2</span><span class="pun">,</span><span class="pln"> </span><span class="lit">3</span><span class="pun">};</span><span class="pln">      
      </span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> f </span><span class="pun">=</span><span class="pln"> e</span><span class="pun">.</span><span class="pln">clone</span><span class="pun">();</span><span class="pln">

      </span><span class="com">//test side effect</span><span class="pln">
      f</span><span class="pun">[</span><span class="lit">0</span><span class="pun">]++;</span><span class="pln">

      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Scenario 3: "</span><span class="pun">);</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Array e: "</span><span class="pun">);</span><span class="pln">
      printArray</span><span class="pun">(</span><span class="pln">e</span><span class="pun">);</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Array f: "</span><span class="pun">);</span><span class="pln">
      printArray</span><span class="pun">(</span><span class="pln">f</span><span class="pun">);</span><span class="pln">

      </span><span class="com">//Scenario 4: Copy array using arraycopy</span><span class="pln">
      </span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> g </span><span class="pun">=</span><span class="pln"> </span><span class="pun">{</span><span class="lit">1</span><span class="pun">,</span><span class="pln"> </span><span class="lit">2</span><span class="pun">,</span><span class="pln"> </span><span class="lit">3</span><span class="pun">};</span><span class="pln">      
      </span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> h </span><span class="pun">=</span><span class="pln"> </span><span class="kwd">new</span><span class="pln"> </span><span class="kwd">int</span><span class="pun">[</span><span class="pln">g</span><span class="pun">.</span><span class="pln">length</span><span class="pun">];</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="pln">arraycopy</span><span class="pun">(</span><span class="pln">g</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> h</span><span class="pun">,</span><span class="pln"> </span><span class="lit">0</span><span class="pun">,</span><span class="pln"> h</span><span class="pun">.</span><span class="pln">length</span><span class="pun">);</span><span class="pln">

      </span><span class="com">//test side effect</span><span class="pln">
      h</span><span class="pun">[</span><span class="lit">0</span><span class="pun">]++;</span><span class="pln">

      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"Scenario 4: "</span><span class="pun">);</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Array g: "</span><span class="pun">);</span><span class="pln">
      printArray</span><span class="pun">(</span><span class="pln">g</span><span class="pun">);</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"Array h: "</span><span class="pun">);</span><span class="pln">
      printArray</span><span class="pun">(</span><span class="pln">h</span><span class="pun">);</span><span class="pln">    
   </span><span class="pun">}</span><span class="pln">

   </span><span class="kwd">public</span><span class="pln"> </span><span class="kwd">static</span><span class="pln"> </span><span class="kwd">void</span><span class="pln"> printArray</span><span class="pun">(</span><span class="kwd">int</span><span class="pun">[]</span><span class="pln"> a</span><span class="pun">)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="str">"[ "</span><span class="pun">);</span><span class="pln">
      </span><span class="kwd">for</span><span class="pln"> </span><span class="pun">(</span><span class="kwd">int</span><span class="pln"> i </span><span class="pun">=</span><span class="pln"> </span><span class="lit">0</span><span class="pun">;</span><span class="pln"> i </span><span class="pun"><</span><span class="pln"> a</span><span class="pun">.</span><span class="pln">length</span><span class="pun">;</span><span class="pln"> i</span><span class="pun">++)</span><span class="pln"> </span><span class="pun">{</span><span class="pln">
         </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="kwd">print</span><span class="pun">(</span><span class="pln">a</span><span class="pun">[</span><span class="pln">i</span><span class="pun">]</span><span class="pln"> </span><span class="pun">+</span><span class="pln"> </span><span class="str">" "</span><span class="pun">);</span><span class="pln">
      </span><span class="pun">}</span><span class="pln">
      </span><span class="typ">System</span><span class="pun">.</span><span class="kwd">out</span><span class="pun">.</span><span class="pln">println</span><span class="pun">(</span><span class="str">"]"</span><span class="pun">);</span><span class="pln">
   </span><span class="pun">}</span><span class="pln">
</span><span class="pun">}</span>

Output

Compile and Run the file to verify the result.

Scenario 1:  
Array a: [ 2 2 3 ]
Array b: [ 2 2 3 ]
Scenario 2:  
Array c: [ 1 2 3 ]
Array d: [ 2 2 3 ]
Scenario 3:  
Array e: [ 1 2 3 ]
Array f: [ 2 2 3 ]
Scenario 4:  
Array g: [ 1 2 3 ]
Array h: [ 2 2 3 ]