java配列

int[] a; // 初期化しない
int[] a = new int[5]; // ０で初期化
int[][] a = new int[2][3]; // 二次元配列

int[] a = {1, 2, 3};  // 長さ3
int[][] a = {{1,2},{3,4}}; // 二次元の初期化
f(new int[]{1, 2, 3}); // 関数の引数として by @saka1029

a.length
a[0].length // 二次元の場合

a[n];
a[i][j]; // 二次元の場合

import java.util.Arrays;

class Rec{
    String str;
    public Rec(String s){str=s;}
    public String toString(){return str;}
}
public class Main
{
    public static void main(String[] args) {
        int[] a = {1,2,3};
        int[] b = a.clone();
        a[1] = 7;
        System.out.println("a=" + Arrays.toString(a) + " b=" + Arrays.toString(b));

        String[] c = {"a", "b", "c"};
        String[] d = c.clone();
        c[1] = "7";
        System.out.println("c=" + Arrays.toString(c) + " d=" + Arrays.toString(d));

        Rec[] e = {new Rec("e"), new Rec("f"), new Rec("g")};
        Rec[] f = e.clone();
        Rec[] g = new Rec[3];
        Rec[] h = Arrays.copyOf(e, 5);
        Rec[] i = Arrays.copyOfRange(e, 2, 4);

        System.arraycopy(e, 0, g, 0, g.length);
        e[0] = new Rec("7");
        e[1].str ="8";
        g[2].str = "9";
        System.out.println("e=" + Arrays.toString(e) + " f=" + Arrays.toString(f) 
            + " g=" + Arrays.toString(g) + " h=" + Arrays.toString(h) + " i=" + Arrays.toString(i));
    }
}

a=[1, 7, 3] b=[1, 2, 3]　             <== b[1]は2のまま
c=[a, 7, c] d=[a, b, c]               <== d[1]はbのまま
e=[7, 8, 9] f=[e, 8, 9] g=[e, 8, 9] h=[e, 8, 9, null, null] i=[9, null]　　<== f[0]はeのまま、f[1], g[1] は変わる、e[2],f[2],g[2]は変わる

for(int i=0; i<a.length; i++){
  // do sth. here
}

import java.util.Arrays;

int[] a = {1,2,3};
System.out.prontln("a=" + Arrays.toString(a));

int[][][] j = {{{1,2},{3,4},{5,6}},{ {7,8},{9,10},{11,12}}};
System.out.println("j=" + j + " aj=" + Arrays.toString(j) + " deepJ=" + Arrays.deepToString(j));

a=[1, 2, 3]  
j=[[[I@2a139a55 aj=[[[I@15db9742, [[I@6d06d69c] deepJ=[[[1, 2], [3, 4], [5, 6]], [[7, 8], [9, 10], [11, 12]]]