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Java Statements: Controlling which section of the code should be executed. You can have condition and then execute it.
If Statement: Conditional Code execution.
public class Welcome { public static void main(String[] args) { int i=10; int y=5; if(i>y){ System.out.println("Print 1 : Here I > Y "); y=11; } System.out.println("Print 2 : Value of I = " + i + " Value of Y = " + y); if(y>i){ System.out.println("Print 3 : Here Y > I "); } //Code will never enter in if condition block as it is always evaluated to false. if(i>y){ System.out.println("Print 4 : Print Here I > Y "); y=11; } if(y>i) System.out.println("Print 5 : Here Y > I "); System.out.println("Print 6 : End of Program"); } } |
If-else statement: Conditional code branching.
public class Welcome { public static void main(String[] args) { int i=10; int y=5; if(i>y){ System.out.println("Print 1 : Here I > Y "); y=11; System.out.println("Print 2 : Value of I = " + i + " Value of Y = " + y); } else if(y>i){ //This else block will never be executed. Even condition is true. System.out.println("Print 3 : Here Y > I "); } //Code will never enter in if condition block as it is always evaluated to false. if(i>y){ System.out.println("Print 4 : Print Here I > Y "); y=11; } else System.out.println("Print 5 : Here Y > I "); //Code will never enter in if condition block as it is always evaluated to false. if(i>y){ System.out.println("Print 6 : Print Here I > Y "); y=11; } else if(y>i) System.out.println("Print 7 : Here Y > I "); /*if(int val=5){ //Will not compile System.out.println("Print 8 "); }*/ System.out.println("Print 9 : End of Program"); } } |
Ternary Operator: (? : ) : This can work on up to three expression. It is equivalent to if-then-else block.
(Always a Boolean expression) ? (If Boolean expression is true then this section) : (if Boolean expression is false then this section) |
public class Welcome { public static void main(String[] args) { //if then else example int y = 20; int x = 0; if (y > 5) { x = 3 * y; } else { x = 4 * y; } System.out.println("Value of x = " + x + " Value of y = " + y); //Ternary operator y=20; x=0; int result = (y>5) ? x= 3*y : 4*y; System.out.println("Value of x = " + x + " Value of y = " + y + " And result = " + result); //Behaves like short circuit operator int val1 = 1; int val2 = 1; final int val3 = val2<2 ? val1++ : val2++; System.out.println(val1+","+val2+ ","+ val3); // Outputs 2,1,1 } } |
switch operator: Complex decision making statement.
- is a complex decision-making structure in which a single value is evaluated and fl ow is redirected to the first matching branch (case statement
)
- If no such case statement is found that matches the value, an optional default statement will be called.
- If no such default option is available, the entire switch statement will be skipped.
- Data type of switch value and case value should be same.
- In each case, you must have break; statement.
- Even though the default block was before the case block, only the case block was executed.
- default is only branched to if there is no matching case value for the switch statement, regardless of its position within the switch statement.
- the case statement value must also be a literal, enum constant, or final constant variable.
public class Welcome { public static void main(String[] args) { int monthVal=Integer.parseInt(args[0]); //Also try with removing break statement. switch(monthVal){ case 1 : System.out.println("Jan"); break; case 2 : System.out.println("Feb"); break; case 3 : System.out.println("Mar"); break; case 4 : System.out.println("Apr"); break; default: System.out.println("No proper month value"); case 5 : System.out.println("May"); break; } } } |
public class Welcome { public static void main(String[] args) { String sitename = "HadoopExam"; String www = "www."; String name = "HadoopExam"; String com = ".com"; int value = 0; switch (name) { case "Hadoop": break; case sitename: value = 1; break; case www: value = 2; break; case com: value = 3; break; case 5000: // DOES NOT COMPILE value = 4; break; case 'H': // DOES NOT COMPILE value = 5; break; case Welcome.class: // DOES NOT COMPILE value = 6; break; } } } |
Data types supported by switch
statements include the following: |
int and Integer |
byte and Byte |
short and Short |
char and Character |
int and Integer |
String |
enum values |
while statement: (it is also known as while loop)
- Infinite while loop
public class Welcome { public static void main(String[] args) { while(true){ System.out.println("I am learning Java from HadoopExam.com"); } } } |
- Controlled while loop
public class Welcome { public static void main(String[] args) { int i = 0; while (i < 10) { System.out.println("I am learning Java from HadoopExam.com value of i " + i); i++; } while (i > 10) { //will not pass this condition System.out.println("I am learning Java from HadoopExam.com value of i " + i); i++; } int j=5; while (i > 10 || j<10) { System.out.println("I am learning Java from HadoopExam.com value of i " + i + " And value of j " + j); j++; } while (i < 11 || j<10) { //Infinite loop System.out.println("I am learning Java from HadoopExam.com value of i " + i + " And value of j " + j); j++; //if(j>2000) //uncomment and test again //break; } } } |
do-while loop
- a do-while loop guarantees that the statement or block will be executed at least once.
- It is your choice, which one to use while or do-while.
- It is recommended you use while.
public class Welcome { public static void main(String[] args) { int i = 0; do { i++; } while (false); System.out.println(i); } } |
for statement : another controlled looping.
public class Welcome { public static void main(String[] args) { for(int i=0; i<10; i++){ int j=0; System.out.println("Value of i = " + i + "Value of j = " + j++); } //Both i and j are local variable //System.out.println("Value of J" + j); // j will not be available here. //System.out.println("Value of i" + i); // i will not be available here. } } |
Infinite for loop
public class Welcome { public static void main(String[] args) { for( ; ; ) { System.out.println("Welcome to HadoopExam.com"); } } } |
public class Welcome { public static void main(String[] args) { for( int i=0, j=0; i<10 && j<10 ; ) { System.out.println("Value of i " + i + " Value of j " + j); i++; j++; } } } |
Below code will not compile: Because you are trying re-initialize the j
public class Welcome { public static void main(String[] args) { int j=0; for( int i=0, j=4; i<10 && j<10 ; ) { System.out.println("Value of i " + i + " Value of j " + j); i++; j++; } } } |
Incompatible data type in initialization block:
public class Welcome { public static void main(String[] args) { // This code will not compile. As you can not use different data type. for(long y = 0, int x = 1; x < 5 && y<10; x++, y++) { System.out.print(x + " "); } } } |
for each statement : (It is added only in Java 5.0)
for(datatype instance : collection/array) |
- Collection/array must be iterable : an object whose class implements java.lang.Iterable
public class Welcome { public static void main(String[] args) { int i = 0; for (char c : "HadoopExam".toCharArray()) { System.out.println(c); } } } |
- Array of strings example
public class Welcome { public static void main(String[] args) { int i = 0; for (String siteName : args) { System.out.println(siteName); } } } |
- Iterating over list
import java.util.ArrayList; import java.util.List; public class Welcome { public static void main(String[] args) { List<String> list = new ArrayList<String>(); list.add("HadoopExam.com"); list.add("QuickTechie.com"); list.add("Training4Exam.com"); for (String siteName : list) { System.out.println(siteName); } } } |
- For-each loop is just an compile time enhancements. Once code is compiled java internally convert it into normal for loop.
Nested Loops : Loop inside loop.
public class Welcome { public static void main(String[] args) { for(int i=0; i<5;i++){ for(int j=0;j<3;j++){ System.out.println("Value of i = " + i + " Value of j = " + j); } } } } |
Formatted output of nested loops.
public class Welcome { public static void main(String[] args) { for(int i=0; i<5;i++){ for(int j=0;j<3;j++){ System.out.print(i+","+j + "\t"); } System.out.println(); } } } |
break statement : Break the loop and come out of the loop
- You can use in any loop this break statement while, for, for-each, do-while etc.
public class Welcome { public static void main(String[] args) { int j=0; for(int i=0; i<5;i++){ System.out.println("Value of i " + i); j++; if(j>3) { break; } } } } |
continue statement :
public class Welcome { public static void main(String[] args) { int j=0; for(int i=0; i<5;i++){ j++; if(j==3) { continue; } System.out.println("Value of i " + i + " Value of j " + j); } } } |
public class Welcome { public static void main(String[] args) { int j=0; for(int i=0; i<5;i++){ if (i<3){ continue; } System.out.println("Inside while loop : value of i = " + i); } } } |
- While the break statement transfers control to the enclosing statement
- the continue statement transfers control to the boolean expression that determines if the loop should continue. it ends the current iteration of the loop.
public class Welcome { public static void main(String[] args) { FIRST_LOOP: for (int count = 1; count <= 4; count++) { for (char seq = 'a'; seq <= 'c'; seq++) { if (count == 2 || seq == 'b') continue FIRST_LOOP; System.out.print(" " + count + seq); } } } } |
