JAVA: Summary / Basic Syntax 95
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Comments //Single line comment /* Multi line comment */
Print System.out.println("Hello " + name);
Exceptions try { .. } catch(Exception e) { ... }
Statements
● Conditional if, switch, VARIABLE = CONDITION ? TRUE : FALSE
● Loop for, while, do
● Jump break, continue, return
Operators
● Comparison compare values of two variables
● Arithmetic perform mathematical operations
● Assignment assign value to variable
● Bitwise combine bits within one or two int or long values
● Logical combine boolean values that can be only TRUE or FALSE
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Comments
//Single line comment.
/* Multi line
comment. */
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Print
//DECLARE VARIABLES.
String name = "John";
int age = 20;
//DISPLAY VARIABLES.
System.out.println("Hello " + name); //Hello John (Concatenation)
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MyClass.java
public class Test {
public static void main(String[] args) {
try{
Integer i = null;
i.byteValue(); //Throws Exception (calling Method on a null Object)
}
catch(Exception e){
System.out.println(e.toString());
}
}
}
JAVA: Summary / Basic Syntax 96
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if (evaluates over different Variables/Conditions)
if (age == 20 ) { System.out.println("Jonh is 20" ); }
else if (name == "John" ) { System.out.println("Name is John"); }
else if (name.equals("Bill")) { System.out.println("Name is Bill"); }
else { System.out.println("No match" ); }
switch (evaluates over the same Variable/Condition)
switch (name) {
case "John":
System.out.println("Name is John");
break; //Without break all below cases are also executed.
case "Bill":
System.out.println("Name is Bill"); //There can be multiple commands inside each case
System.out.println("Found Bill");
break;
default:
System.out.println("No match");
}
VARIABLE = CONDITION ? TRUE : FALSE (simplified assignment)
//TEST VARIABLES.
int a = 10;
int b = 5;
//VARIABLE = CONDITION ? TRUE : FALSE
int max = (a > b) ? a : b;
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for
//SIMPLE
for(int i=1; i<5; i++) { System.out.println(i); }
//COMPLEX
for(int i=1, j=5; i<5 && j>2; i++, j--) {
System.out.println(i);
}
while
int i = 1;
while(i<5) {
i++;
System.out.println(i);
}
do
int i = 1;
do {
i++;
System.out.println(i);
} while(i<5);
JAVA: Summary / Basic Syntax 97
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break (break from loop)
//FOR (WHILE, DO)
for(int i=1; i<5; i++) {
if(i==3) { break; } //Break from Loop.
System.out.println(i); //1, 2
}
//SWITCH
int i = 1;
switch (i) {
case 1:
System.out.println("CASE 1"); //Only selected case is executed.
break; //Exit Switch. Or it will go to next case.
default:
System.out.println("CASE Default");
}
continue (continue with next iteration)
//FOR (WHILE, DO)
for(int i=1; i<5; i++) {
if(i==3) { continue; } //Continue with next loop iteration (skips subsequent lines)
System.out.println(i); //1, 2, 4 (missing 3)
}
return (return from method)
public class Test {
//DECLARE METHOD.
static String test() {
return("Hello"); //Return string.
}
//CALL METHOD.
public static void main(String[] args) {
String result = test(); //Store function's return value into variable result.
System.out.println(result);
}
}
JAVA: Summary / Basic Syntax 98
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Comparison Operators (for Numerical values)
//FOR char, byte, short, int, long, float, double.-------------------------------------------------
char left = 65;
long right = 70;
if (left == right) { System.out.println("Left equals right."); } // Equal
if (left != right) { System.out.println("Left is different from right."); } // Not equal
if (left < right) { System.out.println("Left is smaller then right."); } // Less than
if (left <= right) { System.out.println("Left is smaller or equals right."); } // Less than or equal
if (left > right) { System.out.println("Left is greater then right."); } // Greater than
if (left >= right) { System.out.println("Left is greater or equals right."); } // Greater than or equal
//FOR boolean.-------------------------------------------------------------------------------------
boolean l = true;
boolean r = false;
if (l == r) { System.out.println("Left equals right."); }
if (l != r) { System.out.println("Left is different from right."); }
Comparison Operators (for Objects and Strings)
//FOR Objects.-------------------------------------------------------------------------------------
String text = "Hello";
if (text instanceof String) { System.out.println("Object is of class String."); }
//FOR Strings.-------------------------------------------------------------------------------------
String text = "Hello";
if (text.equals ("Hello")) { System.out.println("text is equal to \"Hello\"." ); }
if (text.equalsIgnoreCase("hello")) { System.out.println("text is equal to \"hello\"." ); }
if (text.contains ("llo" )) { System.out.println("text contains \"llo\"." ); }
if (text.contentEquals ("Hello")) { System.out.println("text is equal to \"Hello\"." ); }
if (text.startsWith ("He" )) { System.out.println("text starts with \"He\"." ); }
if (text.startsWith ("llo",2)) { System.out.println("text at index 2 starts with \"llo\"."); }
if (text.endsWith ("llo" )) { System.out.println("text ends with \"llo\"." ); }
if (text.matches ("Hello")) { System.out.println("text matches regex \"Hello\"." ); }
Arithmetic Operators (perform mathematical operations)
//TEST VARIABLES.
int x = 10;
int y = 20;
//ARITHMETIC OPERATORS.
int plus = +y; //+10 = +10
int negate = -y; //-10 = -10
int add = x+y; //10+20 = 30
int subtract = x-y; //10-20 = -10
int multiply = x*y; //10*20 = 200
int divide1 = x/y; //10/20 = 0.5 = 0
float divide2 = (float)x/y; //10.0/20.0 = 0.5
int reminder = x%y; //10%20 = 0*20+10 = 10
int increment1 = ++x; //Increment x by 1 and then store x into increment1.
int decrement1 = --x; //Decrement x by 1 and then store x into decrement1.
int increment2 = x++; //Store x into increment2 and then increment x by 1.
int decrement2 = x--; //Store x into decrement2 and then decrement x by 1.
JAVA: Summary / Basic Syntax 99
Assignment Operators (assign value to variable)
int x = 10; // Assignment
x += 10; // Addition-Assignment x = x + 10
x -= 10; // Subtraction-Assignment x = x - 10
x *= 10; // Multiplication-Assignment x = x * 10
x /= 10; // Division-Assignment x = x / 10
x %= 10; // Modulus-Assignment x = x % 10
Bitwise Operators (combine bits within one or two int or long values)
//TEST VARIABLES.
int left = Integer.parseInt ("11011", 2);
int right = Integer.parseInt ("10010", 2);
//BITWISE OPERATORS.
int and = left & right; //10010. 1 if both bits are 1.
int or = left | right; //11011. 1 if either bit is 1.
int xor = left ^ right; //01001. 1 if bits are different.
int invert = ~left; //00100. Invert bits.
int shiftLeft = left << 3; //11011000. Shift bits to the left by 3. Fill with 0.
int shiftRight = left >> 2; //110. Shift bits to the right by 2. Fill with 0.
int shiftRight2 = left >>> 2; //????
//DISPLAY RESULTS.
System.out.println (Integer.toBinaryString(and)); //Display in Binary Format
Logical Operators (combine boolean values)
//TEST VARIABLES.
char left = 65;
long right = 70;
//LOGICAL OPERATORS.
if ( left> 50 && right==70 ) { System.out.println("Both are true" ); } // AND
if ( left> 50 AND right==70 ) { System.out.println("Both are true " ); } // AND
if ( left!=4 || right> 90 ) { System.out.println("At least one is true" ); } // OR
if ( left!=4 OR right> 90 ) { System.out.println("At least one is true " ); } // OR
if ( left!=4 XOR right> 90 ) { System.out.println("Only one is true ); } // XOR
if ( ! (left==80)) { System.out.println("left is NOT equal to 80" ); } // NOT
if ( NOT (left==80)) { System.out.println("left is NOT equal to 80" ); } // NOT
