Arrays in Java

In Java array is a collection of elements of same type. The array cannot be resized dynamically, for this use any list class, for example ArrayList

Square brackets [] are used to declare an array and as an element access operator.

The Arrays class contains some useful utility methods to handle arrays. For fast copying one array to another you can use the System.arraycopy() method.

 // array declaration
String a [];
String [] a1;

// array declaration with initialization
String a2 [] = new String[2]; // empty array, every element is null 
String a3 [] = new String[] {"str1", null, "str2"}; // with elements


//  array with elements of primitive type
int nums [] = new int [] {1,2,3};
int nums1 [] = new int[3]; // every element zero 

// access to element, elements are indexed from 0
String s = a3[0];
String s1 = a3[1];

// change value
a3[2] = "some new value";

// assign new array to the variable
a2 = a3;

iterate over array

// iterate over array
for(String el: a3){
    System.out.println(el);
}
    
// iterate over array by index   
for(int i=0; i<a3.length; ++i){
     System.out.println(a3[i]);
}

// iterate via stream
Arrays.stream(a3).forEach(el -> System.out.println(el));

compare arrays

if(Arrays.equals(intArray1,intArray2)){
    // ...
}

// deep compare
if(Arrays.deepEquals(objArray1,objArray2)){
    // ...
}

array/list conversion

String[] strArray = { "a", "b", "c", "d", "e" };
        
// array to list
List<String> strList = Arrays.asList(strArray);
        
// list to array
String [] strArray2 = new String[strList.size()];
strList.toArray(strArray2);

Arrays class