Single Function in Java to Check NULL value or object

import javax.swing.*;  
public class FirstSwingExample {  
public static void main(String[] args) {  
JFrame f=new JFrame();//creating instance of JFrame  
          
JButton b=new JButton("click");//creating instance of JButton  
b.setBounds(130,100,100, 40);//x axis, y axis, width, height  
          
f.add(b);//adding button in JFrame  
          
f.setSize(400,500);//400 width and 500 height  
f.setLayout(null);//using no layout managers  
f.setVisible(true);//making the frame visible  
}  
}  

List<String> songList = new ArrayList<>();
songList.add("Some song"); //Repeat until satisfied

System.out.println("\n\tWelcome! Please choose a song!");
String songChoice = scan.nextLine();
while (!songList.contains(songChoice)) {
    //Do stuff when input is not a recognised song
}

String[][] deepArray = new String[][] {{"John", "Mary"}, {"Alice", "Bob"}};
System.out.println(Arrays.toString(deepArray));
//output: [[Ljava.lang.String;@106d69c, [Ljava.lang.String;@52e922]
System.out.println(Arrays.deepToString(deepArray));

Map<String, String> map = ...
for (Map.Entry<String, String> entry : map.entrySet()) {
    System.out.println(entry.getKey() + "/" + entry.getValue());
}

import java.util.Stack;

/**
 * Java Program to implement a binary search tree. A binary search tree is a
 * sorted binary tree, where value of a node is greater than or equal to its
 * left the child and less than or equal to its right child.
 * 
 * @author WINDOWS 8
 *
 */
public class BST {

    private static class Node {
        private int data;
        private Node left, right;

        public Node(int value) {
            data = value;
            left = right = null;
        }
    }

    private Node root;

    public BST() {
        root = null;
    }

    public Node getRoot() {
        return root;
    }

    /**
     * Java function to check if binary tree is empty or not
     * Time Complexity of this solution is constant O(1) for
     * best, average and worst case. 
     * 
     * @return true if binary search tree is empty
     */
    public boolean isEmpty() {
        return null == root;
    }

    
    /**
     * Java function to return number of nodes in this binary search tree.
     * Time complexity of this method is O(n)
     * @return size of this binary search tree
     */
    public int size() {
        Node current = root;
        int size = 0;
        Stack<Node> stack = new Stack<Node>();
        while (!stack.isEmpty() || current != null) {
            if (current != null) {
                stack.push(current);
                current = current.left;
            } else {
                size++;
                current = stack.pop();
                current = current.right;
            }
        }
        return size;
    }


    /**
     * Java function to clear the binary search tree.
     * Time complexity of this method is O(1)
     */
    public void clear() {
        root = null;
    }

}

private boolean oneQueenPerRow() {
    int foundQueens;
    for (int i = 0; i < board.length; i++) {
        foundQueens = 0;//each loop is a checked row
        for (int j = 0; j < board.length; j++) {
            if (board[i][j] == QUEEN)
                foundQueens++;
        }
        if (foundQueens > 1) return false;
    }
    return true;
}

public <T> List<Class<? extends T>> findAllMatchingTypes(Class<T> toFind) {
    foundClasses = new ArrayList<Class<?>>();
    List<Class<? extends T>> returnedClasses = new ArrayList<Class<? extends T>>();
    this.toFind = toFind;
    walkClassPath();
    for (Class<?> clazz : foundClasses) {
        returnedClasses.add((Class<? extends T>) clazz);
    }
    return returnedClasses;
}

import java.io.*;
import java.util.*;

class GFG 
{
	static int maxCuts(int n, int a, int b, int c)
	{
		if(n == 0) return 0;
		if(n < 0)  return -1;

		int res = Math.max(maxCuts(n-a, a, b, c), 
		          Math.max(maxCuts(n-b, a, b, c), 
		          maxCuts(n-c, a, b, c)));

		if(res == -1)
			return -1;

		return res + 1; 
	}
  
    public static void main(String [] args) 
    {
    	int n = 5, a = 2, b = 1, c = 5;
    	
    	System.out.println(maxCuts(n, a, b, c));
    }
}

<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <gradient
        android:angle="45"
        android:startColor="#ff00ff"
        android:endColor="#000000"/>
</shape>

for(int i = 0; i < 108; i++) {
System.out.println('Jai Shri Ram!');
}

// IntendedActivity - the file you wish to open
// CurrentActivity - the file where this code is placed  

Intent intent = new Intent (this, IntendedActivity.class);
    CurrentActivity.this.startActivity(intent);

 public void sort(int array[]) { 
     for (int i = 1; i < array.length; i++) { 
          int key = array[i]; 
          int j = i - 1; 
          while (j >= 0 && array[j] > key) { 
              array[j + 1] = array[j]; 
              j = j - 1; 
          } 
          array[j + 1] = key; 
      } 
 }

public class LocalDatabase extends SQLiteOpenHelper {
         
    private static final String mDatabaseName = "LocalDatabase";
    private static final int mDatabaseVersion = 1;

public LocalDatabase(Context context) {
        super(context, mDatabaseName, null, mDatabaseVersion);
        SQLiteDatabase db = this.getWritableDatabase();
    }      

}

    AlarmManager alarmManager;

class Main
{
	static int totalWeight = 0;
    // A class to represent a graph edge
    class Edge implements Comparable<Edge>
    {
        int src, dest, weight;
 
        // Comparator function used for sorting edges based on
        // their weight
        public int compareTo(Edge compareEdge)
        {
            return this.weight-compareEdge.weight;
        }
    };
 
    // A class to represent a subset for union-find
    class subset
    {
        int parent, rank;
    };
 
    int V, E;	// V-> no. of vertices & E->no.of edges
    Edge edge[]; // collection of all edges
 
    // Creates a graph with V vertices and E edges
    Main(int v, int e)
    {
        V = v;
        E = e;
        edge = new Edge[E];
        for (int i=0; i<e; ++i)
            edge[i] = new Edge();
    }
 
    // A utility function to find set of an element i
    // (uses path compression technique)
    int find(subset subsets[], int i)
    {
        // find root and make root as parent of i (path compression)
        if (subsets[i].parent != i)
            subsets[i].parent = find(subsets, subsets[i].parent);
 
        return subsets[i].parent;
    }
 
    // A function that does union of two sets of x and y
    // (uses union by rank)
    void Union(subset subsets[], int x, int y)
    {
        int xroot = find(subsets, x);
        int yroot = find(subsets, y);
 
        // Attach smaller rank tree under root of high rank tree
        // (Union by Rank)
        if (subsets[xroot].rank < subsets[yroot].rank)
            subsets[xroot].parent = yroot;
        else if (subsets[xroot].rank > subsets[yroot].rank)
            subsets[yroot].parent = xroot;
 
        // If ranks are same, then make one as root and increment
        // its rank by one
        else
        {
            subsets[yroot].parent = xroot;
            subsets[xroot].rank++;
        }
    }
 
    // The main function to construct MST using Kruskal's algorithm
    void KruskalMST()
    {
        Edge result[] = new Edge[V];  // Tnis will store the resultant MST
        int e = 0;  // An index variable, used for result[]
        int i = 0;  // An index variable, used for sorted edges
        for (i=0; i<V; ++i)
            result[i] = new Edge();
 
        // Step 1:  Sort all the edges in non-decreasing order of their
        // weight.  If we are not allowed to change the given graph, we
        // can create a copy of array of edges
        Arrays.sort(edge);
 
        // Allocate memory for creating V ssubsets
        subset subsets[] = new subset[V];
        for(i=0; i<V; ++i)
            subsets[i]=new subset();
 
        // Create V subsets with single elements
        for (int v = 0; v < V; ++v)
        {
            subsets[v].parent = v;
            subsets[v].rank = 0;
        }
 
        i = 0;  // Index used to pick next edge
 
        // Number of edges to be taken is equal to V-1
        while (e < V - 1)
        {
            // Step 2: Pick the smallest edge. And increment the index
            // for next iteration
            Edge next_edge = new Edge();
            next_edge = edge[i++];
 
            int x = find(subsets, next_edge.src);
            int y = find(subsets, next_edge.dest);
 
            // If including this edge does't cause cycle, include it
            // in result and increment the index of result for next edge
            if (x != y)
            {
                result[e++] = next_edge;
                Union(subsets, x, y);
            }
            // Else discard the next_edge
        }
        int totalMSTWeight = 0;
        


        
        for (i = 0; i < e; ++i) {
        		totalMSTWeight += result[i].weight;
        }
//        System.out.println("total " + totalWeight);
//        System.out.println("MST " + totalMSTWeight);
        System.out.println(totalWeight - totalMSTWeight);
    }
 
    // Driver Program
    public static void main (String[] args) throws Exception
    {
    		BufferedReader br = new BufferedReader (new InputStreamReader(System.in));
    		String in = br.readLine();
    		
    		while (!in.equals("0 0")) {
    			totalWeight = 0;
    			String [] split = in.split(" ");
        		int V = Integer.parseInt(split[0]);
        		int E = Integer.parseInt(split[1]);

            Main graph = new Main(V, E);
            
            for (int i=0; i<E; i++) {
            		in = br.readLine();
            		//System.out.println("split2: " + in);
            		String [] split2 = in.split(" ");
            		int a = Integer.parseInt(split2[0]);
            		int b = Integer.parseInt(split2[1]);
            		int c = Integer.parseInt(split2[2]);
            		
            		graph.edge[i].src = a;
            		graph.edge[i].dest = b;
            		graph.edge[i].weight = c;
            		
            		totalWeight += c;
            		//System.out.println("source: "+a+", dest: " + b + " weight: "+ c);
            }
            graph.KruskalMST();
            in = br.readLine();
    		}
    }
}