JavaSE - JDK1.5 new features

1. Variable parameters

Requirements: To a design method for an arbitrary integer parameter addition result calculation, early implementations (array):

public class Test{
    public static void main(String[] args) {
        System.out.println(add(new int[]{1}));
        System.out.println(add(new int[]{1,2,3}));
        System.out.println(add(new int[]{1,4,6}));
        System.out.println(add(new int[]{1,1,3,4,4}));
    }

    public static int add(int[] data){
        int result = 0;
        for (int i = 0; i < data.length; i++) {
            result += data[i];
        }
        return result;
    }
}

JDK1.5 added after 可变参数the concept defined in the following format:

publlic [static] [final] 返回值 方法名(参数类型 参数名, 参数类型...参数名称){}

The method of the variable parameters to achieve the above requirements:

public class Test{
    public static void main(String[] args) {
        System.out.println(add(1,3,4));//随意传递的内容，随意个数
        System.out.println(add(new int[]{1,2,3}));//可变参数可以接收数组
        System.out.println(add(new int[]{1,4,6}));
        System.out.println(add(new int[]{1,1,3,4,4}));
    }

    public static int add(int...data){
        int result = 0;
        for (int i = 0; i < data.length; i++) {
            result += data[i];
        }
        return result;
    }
}

可变参的本质上是数组，一个方法中只允许一个可变参，并且可变参一定是方法最后一个参数, Many types of transmission parameters Example:

public class Test{
    public static void main(String[] args) {
        System.out.println(add("Hello"));
        System.out.println(add("Hello",1,4,5,6));
        System.out.println(add("Hello",new int[]{1,2,3}));
    }
    public static int add(String msg,int ... data) {
        int result = 0 ;
        for (int i = 0; i < data.length; i++) {
            result += data[i] ;
        }
        return result ;
    }
}

2.foreach (Enhanced for loop)

Used for the original array output cycle is complete, for example:

public class Test{
    public static void main(String[] args) {
        int[] data = new int[] { 1, 2, 3, 4, 5 }; // 原始数组
        for (int i = 0; i < data.length; i++) {
            System.out.println(data[i]); // 通过循环控制索引下标
        }
    }
}

foreach syntax:

for(数据类型 临时变量 : 数组(集合)){
	//循环次数为数组长度，而每一次循环都会顺序取出数组中的一个元素赋值给临时变量
}

Examples are as follows:

public class Test {
    public static void main(String[] args) {
        int[] data = new int[] { 1, 2, 3, 4, 5 }; // 原始数组
        for (int i : data) { // 将数组中每个元素赋值给i
            System.out.println(i); // 这种循环避免了角标的问题
        }
    }
}

3. static imports

MyMath categories:

package www.xpu.java.util;
public class MyMath {
    public static int add(int x, int y) {
        return x + y;
    }
    public static int sub(int x, int y) {
        return x - y;
    }
}

MyMath first import the class, then all the static MyMath class by calling
methods:

package www.xpu.java.test;
import www.xpu.java.util.MyMath;

public class TestDemo {
    public static void main(String[] args) {
        System.out.println(MyMath.add(10, 20));
        System.out.println(MyMath.sub(30, 10));
    }
}

JDK1.5 start from, all the static field of a class (static properties including methods), all classes into use, properties and methods to call at this time is no longer required class name can be called directly main methods:

package www.xpu.java.test;
import static www.xpu.java.util.MyMath.*; // 静态导入
public class TestDemo {
    public static void main(String[] args) {
        System.out.println(add(10, 20));
        System.out.println(sub(30, 10));
    }
}

In fact this method is not efficient, the development is not recommended