java interview questions_ Top 20 java interview programs and answers

Passing Array to method in java: We can pass the java array to method so that we can reuse the same logic on any array. Let's see the simple example to get minimum number of an array using method. class Testarray2{ static void min(int arr[]){ int min=arr[0]; for(int i=1;i<arr.length;i++) if(min>arr[i]) min=arr[i];

System.out.println(min); } public static void main(String args[]){ int a[]={33,3,4,5}; min(a);//passing array to method }} Output: 3

Multidimensional array in java: In such case, data is stored in row and column based index (also known as matrix form). Syntax to Declare Multidimensional Array in java: dataType[][] arrayRefVar; (or) dataType [][]arrayRefVar; (or) dataType arrayRefVar[][]; (or) dataType []arrayRefVar[]; Example to instantiate Multidimensional Array in java:

int[][] arr=new int[3] [3];//3 row and 3 column Example to initialize Multidimensional Array in java arr[0][0]=1; arr[0][1]=2; arr[0][2]=3; arr[1][0]=4; arr[1][1]=5; arr[1][2]=6; arr[2][0]=7; arr[2][1]=8; arr[2][2]=9;

Example of Multidimensional java array: Let's see the simple example to declare, instantiate, initialize and print the 2Dimensional array. class Testarray3{ public static void main(String args[]){ //declaring and initializing 2D array int arr[][]={{1,2,3},{2,4,5},{4,4,5}}; //printing 2D array for(int i=0;i<3;i++){ for(int j=0;j<3;j++){ System.out.print(arr[i][j]+\" \");

} System.out.println(); } }} Output:1 2 3 245 445

Loop There may be a situation when you need to execute a block of code several number of times. In general, statements are executed sequentially: The first statement in a function is executed first, followed by the second, and so on. Programming languages provide various control structures that allow for more complicated execution paths. A loop statement allows us to execute a statement or group of statements multiple times and following is the general form of a loop statement in most

of the programming languages − Java programming language provides the following types of loop to handle looping requirements.

While loop: If we want to run a specific statement more than once in a loop, we need another method. To do this, java comes with another couple of keywords, while and for. The while statement is somewhat easier to use. It needs only one bool argument to determine if it should continue to execute. This statement is somewhat like the if statement, only that it returns to the top of the while statement when it’s done with its evaluations.

The syntax of a while loop is : while(Boolean_expression) { // Statements } Here, statement(s) may be a single statement or a block of statements. The condition may be any expression, and true is any non zero value. When executing, if the boolean_expression result is true, then the actions inside the loop will be executed. This will continue as long as the expression result is true. When the condition becomes false,

program control passes to the line immediately following the loop.

Flow Diagram:



Here, key point of the while loop is that the loop might not ever run. When the expression is tested and the result is false, the loop body will be skipped and the first statement after the while loop will be executed.

Example: public class Test { public static void main(String args[]) { int x = 10; while( x < 20 ) { System.out.print(\"value of x : \" + x ); x++; System.out.print(\"\\n\"); }

} } This will produce the following result:

Output: value of x : 10 value of x : 11 value of x : 12 value of x : 13 value of x : 14 value of x : 15 value of x : 16 value of x : 17 value of x : 18 value of x : 19

For Loop: To gain a bit more control over the execution of a loop, we have another option. The for loop requires three different statements to operate. The first statement is called an initialization, the second is a condition, and the third is an operation. Syntax: for(initialization; Boolean_expression; update) { // Statements

} Here is the flow of control in a for loop − The initialization step is executed first, and only once. This step allows you to declare and initialize any loop control variables and this step ends with a semi colon (;). Next, the Boolean expression is evaluated. If it is true, the body of the loop is executed. If it is false, the body of the loop will not be executed and control jumps to the next statement past the for loop. After the body of the for loop gets

executed, the control jumps back up to the update statement. This statement allows you to update any loop control variables. This statement can be left blank with a semicolon at the end. The Boolean expression is now evaluated again. If it is true, the loop executes and the process repeats (body of loop, then update step, then Boolean expression). After the Boolean expression is false, the for loop terminates.

Flow Diagram:



Example: Following is an example code of the for loop in Java. public class Test { public static void main(String args[]) { for(int x = 10; x < 20; x = x + 1) { System.out.print(\"value of x : \" + x ); System.out.print(\"\\n\"); }

} } This will produce the following result:

Output: value of x : 10 value of x : 11 value of x : 12 value of x : 13 value of x : 14 value of x : 15 value of x : 16 value of x : 17 value of x : 18 value of x : 19

Loop Control Statements: Loop control statements change execution from its normal sequence. When execution leaves a scope, all automatic objects that were created in that scope are destroyed. Java supports the following control statements. Break Statement Continue Statement The break statement in Java programming language has the following two usages −

When the break statement is encountered inside a loop, the loop is immediately terminated and the program control resumes at the next statement following the loop. It can be used to terminate a case in the switch statement (covered in the next chapter).

Syntax The syntax of a break is a single statement inside any loop: break;

Flow Diagram:



Example: public class Test { public static void main(String args[]) { int [] numbers = {10, 20, 30, 40, 50}; for(int x : numbers ) { if( x == 30 ) { break; } System.out.print( x );

System.out.print(\"\\n\"); } } } This will produce the following result:

Output 10 20

The continue keyword can be used in any of the loop control structures. It causes the loop to immediately jump to the next iteration of the loop. In a for loop, the continue keyword causes control to immediately jump to the update statement. In a while loop or do/while loop, control immediately jumps to the Boolean expression.

Syntax The syntax of a continue is a single statement inside any loop − continue;

Flow Diagram:



Example: public class Test { public static void main(String args[]) { int [] numbers = {10, 20, 30, 40, 50}; for(int x : numbers ) { if( x == 30 ) { continue; } System.out.print( x );

System.out.print(\"\\n\"); } } } This will produce the following result :

Output 10 20 40 50

Thinking in Algorithms An algorithm is a detailed step-by-step instruction set or formula for solving a problem or completing a task. In computing, programmers write algorithms that instruct the computer how to perform a task. When you think of an algorithm in the most general way (not just in regards to computing), algorithms are everywhere. A recipe for making food is an algorithm, the method you use to solve addition or long division problems is an algorithm, and the process of folding a shirt or a pair of pants is an algorithm. Even your morning routine could be

considered an algorithm! In fact, here’s what your child’s morning might look like written out as an algorithm:



Statements and Expressions When reading a book or story you extract meaning from an ordered chain of words. In a similar way, computers extract commands from a chain of ordered instructions. In English we call this a sentence; programmers call this a statement. A statement is considered to be any chunk of code which accomplishes some sort of task separated by a semicolon. At the center of any given task is the

algorithm, not to be confused with a logarithm. An algorithm is a systematic process that accomplishes something. In many ways you can think of it as a recipe, or rather a recipe is an algorithm for making food. It can take just one or two statements to accomplish a task, or it could take many hundreds of statements.



This all depends on the difficulty of a given task. Each individual statement is a step toward a goal. This is the difference between spending a few minutes frying an egg, or spending an hour baking a souffle. Each step is usually fairly simple; it’s the final result that matters. Like sentences, statements have different forms. Statements can declare and assign values to variables. These are called declaration and assignment statements. These statements are used to set up various types of data and give them names.

Expressions: The subjects of your statements are called identifiers. An assignment statement is used to give an identifier a value. When you read “Jack is a boy and Jill is a girl,” you’ve mentally assigned two subjects their genders. In Java this might look more like: gender Jack = male; gender Jill = female; Assignment statements often incorporate some sort of operation. These are called expressive statements. Different from expressing an emotion, expressions in code look more like “x +

y.” Expressions process data. After processing, the result of an expression can be assigned to a variable. A collection of statements is called a code block, not like a roadblock which might stop your code, but more like a building block, anything that’s used to build. When writing a story, we call a collection of sentences a paragraph. The statements in a block of code work with each other to accomplish a task.

Learning To Copy & Paste “A good artist creates, a great artist steals.” There are code examples for you to copy and paste into your project. The content of this book and all downloadable content are no different. This means that you’ll have to understand what the code is doing to interpret it to fit your needs. Every programmer does this habitually.