[Java Foundation Series] 3 - operators and expressions of Java

1. Operator

1.1 arithmetic operators

• Arithmetic operator: two operands are evaluated

  Operatordescribe+Addition and summation-Subtraction and subtraction*Multiplication and quadrature/Division and quotient%Module and remainder

• Arithmetic operator: unary operator (only one operand)

  Operatordescribe++Increment, variable value + 1–Decrement, variable value - 1

for instance:

public class TestOperation1{ public static void main(String[] args){ int a = 10; int b = 3; System.out.println(a / b); // Quotient = 3 System.out.println(a % b); // Remainder = 1 double d = 10.0; int c = 3; System.out.println(d / c); // Quotient 3.33 int num1 = 10; num1++; //Self increment 1 System.out.println(num1); int num2 = 10; num2--; //Self subtraction 1 System.out.println(num2); int num3 = 5; // priority // First + +: first + +, and then print the self incremented value // After + +: print the current value first, and then++ System.out.println(num3++); //System.out.println(++num3); System.out.println(num3); int num4 = 100; // First + +: first + +, then assignment // After + +: assign values first, and then++ int num5 = num4++; System.out.println(num5); System.out.println(num4); int num6 = 100; // When used alone, there is no difference in priority num6++; //Self increment 1 System.out.println(num6); } }

The execution results are as follows:

1.2 assignment operator

• Assignment operator: assignment from the right side of the equal sign to the left side of the equal sign

Operatordescribe=Direct assignment+=Assignment after summation-=Assignment after difference*=Assignment after quadrature/=Assignment after quotient%=Assignment after remainder

for instance:

public class TestOperation2{ public static void main(String[] args){ int a = 10; // Assignment Operators a += 5; // On the basis of a + 5 > > > A = a + 5; System.out.println(a); int b = 20; b -= 3; // b = b - 3; System.out.println(b); int c = 30; c %= 4; // c = c % 4; System.out.println(c); } }

The execution results are as follows:

1.3 relational operators

• Relational operators: comparing two operands

Operatordescribe>greater than<less than>=Greater than or equal to<=Less than or equal to==be equal to!=Not equal to

for instance:

public class TestOperation3{ public static void main(String[] args){ int a = 10; int b = 6; System.out.println(a > b); System.out.println(a < b); System.out.println(a >= b); System.out.println(a <= b); System.out.println(a == b); System.out.println(a != b); } }

The execution results are as follows:

1.4 logical operators

• Logical operator: logical comparison between operands or expressions of two boolean types

  Operatorsemanticsdescribe&&And (and)Both operands are true at the same time, and the result is true||Or (or)Two operands, one of which is true and the result is true!Non (reverse)True is false, false is true

  for instance:

  public class TestOperation4{ public static void main(String[] args){ int javaScore = 100; int webScore = 99; // Compare whether they are equal System.out.println(javaScore == webScore); // Judge whether both are full marks System.out.println(javaScore == 100); System.out.println(webScore == 100); // Through an expression, judge whether both are full marks // Two expressions are true > > > true at the same time. If one of the two expressions is false > > > false System.out.println(javaScore == 100 && webScore == 100); // Judge whether there is a full score at one time // One is true and the result is true System.out.println(javaScore == 100 || webScore == 100); boolean result = javaScore == 100; // Is Java a full mark? System.out.println(result); // Result > > > true // Isn't Java a full mark? System.out.println(!result); // Result > > > false } }

  The execution results are as follows:

  

1.5 ternary operator

• Ternary operator: assign the judged result to the variable

  Operatorsemanticsdescribe?:Boolean expression? Result 1: result 2When the expression result is true, the result 1 is obtained; When the expression result is false, the result 2 is obtained

For example:

public class TestOperation5{ public static void main(String[] args){ // 1. Judge // 2. Assignment //Syntax: Boolean expression? Value 1: value 2 int javaScore = 100; String result = javaScore == 100 ? "congratulations" : "come on."; System.out.println(result); int webScore = 99; int result2 = webScore == 100?666:111; System.out.println(result2); } }

The execution results are as follows:

2. Expression

• Use operators to connect variables or literals, and you can get a final result

  For example:

  1 + 2 + 3; int a = 2; a - 1; int b = 10; int c = 20; b * c; c / b; short d = 100; int e = 200; d > e; d <= e;

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