关于一些JAVA的基础知识总结

Java 基础

• 有如下两个数组 int a[] = {1,3,5,7,8}; int b[] = {0,3,5,10,20}; 选出属于数组b但不属于数组a的元素

public class TestInt {    public static void main(String[] args) {        int a[] = {1,3,5,7,8};        int b[] = {0,3,5,10,20};        System.out.println(Arrays.toString(find(b,a)));    }    //选出属于数组a但不属于数组b的元素    public static int[] find(int[] a, int[] b){        ArrayList<Integer> list = new ArrayList<Integer>();        for(int i = 0; i < a.length; ++i) {            boolean bContained = false;            for(int j = 0; j < b.length; ++j) {                if (a[i] == b[j]) {                    bContained = true;                    break;                }            }            if (!bContained) {                list.add(a[i]);            }        }        int res[] = new int[list.size()];        for(int i = 0; i < list.size(); ++i){            res[i] = list.get(i);        }        return res;    }}

• 继承、静态的理解

public class TestStaticExtend {    public static void main(String[] args) {        A se = new B();        se.print();    }}class A{    static {        System.out.println("AAAA");    }    public A(){        System.out.println("struc A");    }    void print(){        System.out.println("this is class A");    }}class B extends A{    static{        System.out.println("BBBB");    }    public B(){        System.out.println("struc B");    }    void print(){        System.out.println("this is class B");    }}

结果:

AAAA
BBBB
struc A
struc B
this is class B

• String 的理解

public class TestString {    String str = new String("hello world");    String[] strarr = {"hello world"};    char[] ch = { 'a', 'b', 'c' };    static TestString ex = new TestString();    public static void main(String[] args) {        change(ex.str, ex.ch);        System.out.println(ex.getStr()+ " and " + Arrays.toString(ex.ch));        change(ex.strarr, ex.ch);        System.out.println(ex.strarr[0] + " and " + Arrays.toString(ex.ch));    }    public static void change(String[] str, char[] ch) {            str[0] = "test ok";        ch[0] = 'g';    }    public static void change(String str, char[] ch) {        ex.setStr("test ok");        ch[0] = 'g';    }    public String getStr() {        return str;    }    public void setStr(String str) {        this.str = str;    }}

结果：

test ok and [g, b, c]
test ok and [g, b, c]