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eric-martineric-martin
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Merge pull request eugenp#5603 from sandy03934/master
BAEL-2303 Added code to demonstrate how to replace multiple if statements in Java
2 parents d00efaa + 3c558d6 commit 91ec114

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Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/AddCommand.java

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package com.baeldung.reducingIfElse;
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public class AddCommand implements Command {
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private int a;
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private int b;
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public AddCommand(int a, int b) {
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this.a = a;
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this.b = b;
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}
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@Override
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public Integer execute() {
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return a + b;
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/AddRule.java

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package com.baeldung.reducingIfElse;
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public class AddRule implements Rule {
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private int result;
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@Override
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public boolean evaluate(Expression expression) {
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boolean evalResult = false;
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if (expression.getOperator() == Operator.ADD) {
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this.result = expression.getX() + expression.getY();
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evalResult = true;
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}
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return evalResult;
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}
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@Override
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public Result getResult() {
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return new Result(result);
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Addition.java

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package com.baeldung.reducingIfElse;
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public class Addition implements Operation {
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@Override
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public int apply(int a, int b) {
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return a + b;
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Calculator.java

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package com.baeldung.reducingIfElse;
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public class Calculator {
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public int calculate(int a, int b, String operator) {
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int result = Integer.MIN_VALUE;
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if ("add".equals(operator)) {
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result = a + b;
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} else if ("multiply".equals(operator)) {
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result = a * b;
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} else if ("divide".equals(operator)) {
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result = a / b;
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} else if ("subtract".equals(operator)) {
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result = a - b;
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} else if ("modulo".equals(operator)) {
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result = a % b;
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}
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return result;
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}
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public int calculateUsingSwitch(int a, int b, String operator) {
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int result = 0;
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switch (operator) {
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case "add":
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result = a + b;
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break;
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case "multiply":
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result = a * b;
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break;
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case "divide":
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result = a / b;
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break;
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case "subtract":
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result = a - b;
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break;
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case "modulo":
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result = a % b;
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break;
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default:
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result = Integer.MIN_VALUE;
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}
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return result;
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}
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public int calculateUsingSwitch(int a, int b, Operator operator) {
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int result = 0;
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switch (operator) {
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case ADD:
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result = a + b;
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break;
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case MULTIPLY:
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result = a * b;
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break;
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case DIVIDE:
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result = a / b;
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break;
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case SUBTRACT:
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result = a - b;
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break;
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case MODULO:
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result = a % b;
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break;
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default:
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result = Integer.MIN_VALUE;
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}
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return result;
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}
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public int calculate(int a, int b, Operator operator) {
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return operator.apply(a, b);
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}
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public int calculateUsingFactory(int a, int b, String operation) {
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Operation targetOperation = OperatorFactory.getOperation(operation)
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.orElseThrow(() -> new IllegalArgumentException("Invalid Operator"));
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return targetOperation.apply(a, b);
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}
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public int calculate(Command command) {
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return command.execute();
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Command.java

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package com.baeldung.reducingIfElse;
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public interface Command {
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Integer execute();
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Division.java

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package com.baeldung.reducingIfElse;
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public class Division implements Operation {
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@Override public int apply(int a, int b) {
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return a / b;
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Expression.java

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package com.baeldung.reducingIfElse;
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public class Expression {
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private Integer x;
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private Integer y;
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private Operator operator;
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public Expression(Integer x, Integer y, Operator operator) {
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this.x = x;
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this.y = y;
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this.operator = operator;
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}
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public Integer getX() {
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return x;
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}
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public Integer getY() {
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return y;
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}
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public Operator getOperator() {
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return operator;
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Modulo.java

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package com.baeldung.reducingIfElse;
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public class Modulo implements Operation {
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@Override public int apply(int a, int b) {
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return a % b;
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Multiplication.java

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package com.baeldung.reducingIfElse;
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public class Multiplication implements Operation {
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@Override public int apply(int a, int b) {
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return 0;
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Operation.java

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package com.baeldung.reducingIfElse;
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public interface Operation {
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int apply(int a, int b);
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Operator.java

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package com.baeldung.reducingIfElse;
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public enum Operator {
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ADD {
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@Override
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public int apply(int a, int b) {
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return a + b;
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}
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},
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MULTIPLY {
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@Override
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public int apply(int a, int b) {
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return a * b;
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}
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},
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SUBTRACT {
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@Override
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public int apply(int a, int b) {
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return a - b;
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}
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},
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DIVIDE {
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@Override
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public int apply(int a, int b) {
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return a / b;
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}
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},
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MODULO {
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@Override
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public int apply(int a, int b) {
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return a % b;
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}
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};
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public abstract int apply(int a, int b);
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/OperatorFactory.java

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package com.baeldung.reducingIfElse;
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import java.util.HashMap;
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import java.util.Map;
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import java.util.Optional;
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public class OperatorFactory {
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static Map<String, Operation> operationMap = new HashMap<>();
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static {
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operationMap.put("add", new Addition());
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operationMap.put("divide", new Division());
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operationMap.put("multiply", new Multiplication());
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operationMap.put("subtract", new Subtraction());
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operationMap.put("modulo", new Modulo());
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}
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public static Optional<Operation> getOperation(String operation) {
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return Optional.ofNullable(operationMap.get(operation));
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Result.java

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package com.baeldung.reducingIfElse;
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public class Result {
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int value;
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public Result(int value) {
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this.value = value;
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}
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public int getValue() {
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return value;
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Rule.java

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package com.baeldung.reducingIfElse;
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public interface Rule {
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boolean evaluate(Expression expression);
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Result getResult();
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/RuleEngine.java

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package com.baeldung.reducingIfElse;
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import java.util.ArrayList;
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import java.util.List;
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import java.util.Optional;
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import java.util.stream.Collectors;
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public class RuleEngine {
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private static List<Rule> rules = new ArrayList<>();
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static {
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rules.add(new AddRule());
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}
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public Result process(Expression expression) {
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Rule rule = rules.stream()
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.filter(r -> r.evaluate(expression))
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.findFirst()
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.orElseThrow(() -> new IllegalArgumentException("Expression does not matches any Rule"));
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return rule.getResult();
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}
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}

Diff for: ‎core-java-8/src/main/java/com/baeldung/reducingIfElse/Subtraction.java

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package com.baeldung.reducingIfElse;
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public class Subtraction implements Operation {
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@Override public int apply(int a, int b) {
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return a - b;
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}
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}

Diff for: ‎core-java-8/src/test/java/com/baeldung/reduceIfelse/CalculatorUnitTest.java

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package com.baeldung.reduceIfelse;
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import com.baeldung.reducingIfElse.AddCommand;
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import com.baeldung.reducingIfElse.Calculator;
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import com.baeldung.reducingIfElse.Operator;
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import org.junit.Test;
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import static org.junit.Assert.assertEquals;
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public class CalculatorUnitTest {
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@Test
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public void whenCalculateUsingStringOperator_thenReturnCorrectResult() {
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Calculator calculator = new Calculator();
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int result = calculator.calculate(3, 4, "add");
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assertEquals(7, result);
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}
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@Test
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public void whenCalculateUsingEnumOperator_thenReturnCorrectResult() {
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Calculator calculator = new Calculator();
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int result = calculator.calculate(3, 4, Operator.valueOf("ADD"));
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assertEquals(7, result);
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}
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@Test
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public void whenCalculateUsingCommand_thenReturnCorrectResult() {
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Calculator calculator = new Calculator();
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int result = calculator.calculate(new AddCommand(3, 7));
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assertEquals(10, result);
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}
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}

Diff for: ‎core-java-8/src/test/java/com/baeldung/reduceIfelse/RuleEngineUnitTest.java

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package com.baeldung.reduceIfelse;
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import com.baeldung.reducingIfElse.Expression;
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import com.baeldung.reducingIfElse.Operator;
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import com.baeldung.reducingIfElse.Result;
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import com.baeldung.reducingIfElse.RuleEngine;
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import org.junit.Test;
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import static org.junit.Assert.assertEquals;
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import static org.junit.Assert.assertNotNull;
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public class RuleEngineUnitTest {
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@Test
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public void whenNumbersGivenToRuleEngine_thenReturnCorrectResult() {
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Expression expression = new Expression(5, 5, Operator.ADD);
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RuleEngine engine = new RuleEngine();
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Result result = engine.process(expression);
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assertNotNull(result);
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assertEquals(10, result.getValue());
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}
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}

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