计算Java数组长度函数的方法以及代码分析

/**
* An Example to get the Array Length is Java
*/
public class ArrayLengthJava {
public static void main(String[] args) {
String[] myArray = { "I", "Love", "Music" };
int arrayLength = myArray.length; //array length attribute
System.out.println("The length of the array is: " + arrayLength);
}
}

/**
* An Example to find the Java Array Length using a function
*/
public class ArrayLengthJava {
private static void printArrayLength(String[] myArray) {
if (myArray == null) //to check whether the array is empty or not
{
System.out.println("The length of the array can't be determined.");
} else {
int arrayLength = myArray.length;
System.out.println("The length of the array is: " + arrayLength);
}
}
public static void main(String[] args) {
String[] JavaArray1 = { "I", "Love", "Music" };
String[] JavaArray2 = { "R", "S" };
String[] JavaArray3 = { "1", "2", "3", "4" };
String[] JavaArray4 = { "Java" };
printArrayLength(null);
printArrayLength(JavaArray1);
printArrayLength(JavaArray2);
printArrayLength(JavaArray3);
printArrayLength(JavaArray4);
}
}

无法确定数组的长度。
数组的长度为：3
数组的长度为：2
数组的长度为：4
数组的长度为：1

/**
* An Example that uses Java Array Length to check if the array contains a
* specific value.
*/
public class ArrayLengthJava {
private static boolean arrayContainsValue(String[] myArray,
String lookForValue) {
if (myArray != null) {
int arrayLength = myArray.length;
for (int i = 0; i <= arrayLength - 1; i++) {
String value = myArray[i];
if (value.equals(lookForValue)) {
return true;
}
}
}
return false;
}
public static void main(String[] args) {
String[] JavaArray = { "I", "Love", "Music" };
System.out.println(arrayContainsValue(JavaArray, "Love"));
System.out.println(arrayContainsValue(JavaArray, "Guitar"));
}
}

/** * Reallocates an array with a new size, and copies the contents  
 * * of the old array to the new array.  
 * * @param oldArray the old array, to be reallocated.  
 * * @param newSize  the new array size.  
 * * @return     A new array with the same contents.  
 * */  
private static Object resizeArray (Object oldArray, int newSize) {    
  int oldSize = java.lang.reflect.Array.getLength(oldArray);    
  Class elementType = oldArray.getClass().getComponentType();    
  Object newArray = java.lang.reflect.Array.newInstance(       
      elementType,newSize);    
  int preserveLength = Math.min(oldSize,newSize);    
  if (preserveLength > 0)      
    System.arraycopy (oldArray,0,newArray,0,preserveLength);    
  return newArray;  }    
// Test routine for resizeArray().   
public static void main (String[] args) {    
  int[] a = {1,2,3};    
  a = (int[])resizeArray(a,5);    
  a[3] = 4;    
  a[4] = 5;    
  for (int i=0; i<a.length; i++)      
    System.out.println (a[i]);   
}