java - 键入数组时 for 循环和 for each 循环的区别

Question

public class WeightedQuickUnionUF {
    private int[] id;
    private int[] sz;

    public WeightedQuickUnionUF(int N){
        id = new int[N];
        sz = new int[N];
        for(int i=0;i<N;i++)
            id[i] = i;
        for(int j=0;j<N;j++)
            sz[j] = 1;
    } 

    // find the root of that number
    public int root(int p){
        while(p != id[p])
            // // Follow links to find a root.
            p = id[p];
        return p;
    }

    public int getid(int p){
        return id[p];
    }
    public int getsize(int p){
        return sz[p];
    }

    // print the array
    // I use 2 ways to print the final array, but the results are different
    public void show(){
        for(int ele:id)
            System.out.print(id[ele]+ " ");
        for(int j=0;j<id.length;j++)
            System.out.print(id[j]+ " ");
        System.out.print("\n");
    }
    // link two trees, the root of the smaller one will be linked to the
    // root of the larger one 
    public void union(int p, int q){
        int rootp = root(p);
        int rootq = root(q);
        if(sz[rootp] < sz[rootq]){
            id[rootp] = rootq;
            sz[rootq] += sz[rootp];
        }
        else{
            id[rootq] = rootp;
            sz[rootp] += sz[rootq];
        }
    }
    // test the class I have defined
    public static void main(String args[]){
        WeightedQuickUnionUF test1 = new WeightedQuickUnionUF(10);
        test1.union(6, 0);
        test1.union(1, 7);
        test1.union(7, 9);
        test1.union(8, 9);
        test1.union(8, 5);
        test1.union(4, 2);
        test1.union(9, 3);
        test1.union(4, 0);
        test1.union(3, 0);
        test1.show();
    }
}

我的问题是关于函数 show() 的性能。我使用 2 种方法打印相同的数组，但结果不同。这段代码的正确输出应该是 6 1 4 1 1 1 4 1 1 1，这意味着 for 循环可以给我正确的答案。但是 for each 循环不能做正确的事情。

Answer 1

for-each loop行为并不像您预期​​的那样。也就是说，

for(int ele : id)
    System.out.print(id[ele]+ " ");

应该是这样的(我建议使用大括号)

for (int ele : id) {
    System.out.print(ele + " ");
}