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Last update:   02-11-2021

Lambdas

p193 Anonymous classes are verbose and hard to use.
 
/**
 * Java 8 Lambdas
 * 
 * Anonymous class instance as a function object is ...
 * hard to use.
 */

package com.minte9.effective.lambdas;

import java.util.ArrayList;
import java.util.Collections;
import java.util.Comparator;
import java.util.List;

public class Anonymous {
            
    public static void main(String[] args) {
        
        List<String> words = new ArrayList<>();
        words.add("ccc");
        words.add("a");
        words.add("bb");

        Collections.sort(words, 

            new Comparator<String>() { // - Look Here

                @Override public int compare(String s1, String s2) {
                    return Integer.compare(
                        s1.length(), s2.length()
                    );
                }
            }
        );
        words.forEach(System.out::println);
            // a, bb, cc
    }
}
p194 Java 8 allows us to create instances of functional interfaces using lamdba expressions.
 
/**
 * Java 8 Lambdas
 * 
 * We create instances of functional interfaces using ...
 * lamdba expressions.
 * 
 * Lambdas are similar to anonymous classes, but ...
 * more concise 
 */

package com.minte9.effective.lambdas;

import java.util.ArrayList;
import java.util.Collections;
import java.util.List;

public class Lambdas {
            
    public static void main(String[] args) {
        
        List<String> words = new ArrayList<>();
        words.add("ccc");
        words.add("a");
        words.add("bb");


        // Example 1
        Collections.sort(words,
            (s1, s2) -> Integer.compare(s1.length(), s2.length())
        );
        words.forEach(System.out::println); 
            // a, bb, ccc


        // Example 2
        words.sort(
            (s1, s2) -> Integer.compare(s1.length(), s2.length())
        );
        words.forEach(System.out::println); 
            // a, bb, ccc
    }
}

Enums

p195 Enum example with no lambdas.
 
/**
 * Java 8 Lambdas
 * 
 * Enum example with no Lambdas
 */
package com.minte9.effective.lambdas;

public class EnumsNoLambdas {

    public enum Operation {

        PLUS ('+') { public int run(int x, int y) { return x + y; } },
        MINUS('-') { public int run(int x, int y) { return x - y; } },
        ;

        private char ch;
        private Operation(char ch) { this.ch = ch; }
        public String toString() { return ch + ""; }
        public abstract int run(int x, int y);

    }

    public static void main(String[] args) {
        
        int a = Operation.PLUS.run(1, 2);
        int b = Operation.MINUS.run(20, 10);

        System.out.println(a); // 3
        System.out.println(b); // 10

        System.out.println(Operation.PLUS); // +
        System.out.println(Operation.MINUS); // -
    }
}
Enum example with lambdas.
 
/**
 * Enum Example - With lambdas
 * 
 * The constructor stores the lambda in an instanced field
 * Later, the method run() invokes the lambda expression
 */

package com.minte9.effective.lambdas;
import java.util.function.IntBinaryOperator;

public class EnumLambdas {

    public enum Operation {

        PLUS  ('+', (x, y) ->  x + y) {},
        MINUS ('-', (x, y) ->  x - y) {};

        IntBinaryOperator op;
        private Operation(char ch, IntBinaryOperator op) { this.op = op; }
        public int run(int x, int y) { return op.applyAsInt(x, y); }
    }

    public static void main(String[] args) {

        int a = Operation.PLUS.run(1, 2);
        int b = Operation.MINUS.run(20, 10);

        System.out.println(a); // 3
        System.out.println(b); // 10
    }
}

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