「もう参照渡しとは言わせない 2018 冬」用　サンプルコード

R.java

import java.util.*;

public class R {
    
    public static void main(String[] args) {
        List<String> x = new ArrayList<>();
        System.out.printf("x: %s\n", x);  // "x: []"
        add(x);
        System.out.printf("x: %s\n", x);  // "x: ["xxx"]"
    }

    public static void add(List<String> a) {
        a.add("xxx");
    }
}

reference.c

// pseudocode
swap(int a, int b) {
    int tmp = a
    a = b
    b = tmp
}

x = 1
y = 2
swap(x, y)
// x = 2, y = 1

Reference.java

import java.util.*;

public class Reference {
    
    public static void main(String[] args) {
        List<String> x = List.of("aaa");
        List<String> y = List.of("bbb");
        System.out.printf("x: %s, y: %s\n", x, y);  // "x: ["aaa"], y: ["bbb"]"
        swap(x, y);
        System.out.printf("x: %s, y: %s\n", x, y);  // "x: ["aaa"], y: ["bbb"]"
    }

    public static void swap(List<String> a, List<String> b) {
        List<String> tmp = a;
        a = b;
        b = tmp;
    }
}

value.c

// pseudocode
swap(int a, int b) {
    int tmp = a
    a = b
    b = tmp
}

x = 1
y = 2
swap(x, y)
// x = 1, y = 2

Value.java

public class Value {
    
    public static void main(String[] args) {
        int x = 1;
        int y = 2;
        System.out.printf("x: %d, y: %d\n", x, y);  // "x: 1, y: 2"
        swap(x, y);
        System.out.printf("x: %d, y: %d\n", x, y);  // "x: 1, y: 2"
    }

    public static void swap(int a, int b) {
        int tmp = a;
        a = b;
        b = tmp;
    }
}