Frame13.java

package lesson3;

public class Frame13 {

	public static void main(String[] args) {
		
		int[] data1 = {2, 44, 4, 44, 2, 33, 1, 77};
		int[] data2 = {0};
		int[] data3 = {0, 0, 0, 0, 0};
		System.out.println(oddElementSum(data1));
		System.out.println(oddElementSum(data2));
		System.out.println(oddElementSum(data3));
	}
	
	static long oddElementSum(int[] data) {
		
		long sum = 0;
		
		if (data.length > 1) {
			for (int i = 1; i < data.length; i +=2){
				sum = data[i] + sum;
			}
			return sum;
		}
		else return -1;
	}
}

Frame15.java

package lesson3;

public class Frame15 {

	public static void main(String[] args) {
		
		System.out.println(average(new int[] {32, 2, 2}));
		System.out.println(average(new int[] {0, 0, 3}));
		System.out.println(average(new int[] {0}));
		System.out.println(average(new int[] {}));
	}
	
	static double average(int[] data) {
		
		double sum = 0;
		
		if (data.length > 0) {
			for (int dat : data) {
				sum = dat + sum;
			}
			return sum / data.length;
		}
		else return -1;
	}
}

Frame16.java

package lesson3;

import java.util.Arrays;

public class Frame16 {

	public static void main(String[] args) {
		
		int[] stack1 = {1, 2, 3, 4};
		int[] stack2 = {2, 22, 33, 44, 55};
		swap(stack1);
		swap(stack2);
		System.out.println(Arrays.toString(stack1));
		System.out.println(Arrays.toString(stack2));
	}
	
	static void swap(int[] data) {
		
		int perm;
		
		if (data.length > 0) {
			for(int i = 0; i < data.length - 1; i++) {
				perm = data[i];
				data[i] = data[i+1];
				data[i+1] = perm;
			}
		}
	}
}

Frame17.java

package lesson3;

import java.util.Arrays;

public class Frame17 {

	public static void main(String[] args) {
		
		int[] stack1 = {1, 2, 3, 4};
		int[] stack2 = {66, 22, 33, 44, 55};
		swap(stack1);
		swap(stack2);
		System.out.println(Arrays.toString(stack1));
		System.out.println(Arrays.toString(stack2));
	}
	
	static void swap(int[] data) {
		
		int perm;
		
		if (data.length > 0) {
			for(int i = 0; i < data.length - 1; i++) {
				if (data[i] > data[i+1]) {
				perm = data[i];
				data[i] = data[i+1];
				data[i+1] = perm;
				}
			}
		}
	}
}