读完部分effective java 自己写的类Entity

自己写的Entity类，有四个属性，int，char，Sting，double，用了构造器方法，可以四个参数都有，也可以之后几个，但int是必须的。类还实现了comparable接口，重写了compareTo，equals，hashCode三个方法，这是我能想到的比较OK的类。

compareTo的比较方法是按int>char>String>double的顺序
equals方法中规中矩，比较而已
hashCode用的书中的方法,待思考

package com.util;

public class Entity implements Comparable{

	private final int i;
	private final char c;
	private final String s;
	private final double d;
	
	public static class Builder {
		private final int i;
		private char c;
		private String s;
		private double d;
		public Builder(int i) {
			this.i = i;
		}
		public Builder setC(char c) {
			this.c = c;
			return this;
		}
		public Builder setS(String s) {
			this.s = s;
			return this;
		}
		public Builder setD(double d) {
			this.d = d;
			return this;
		}
		public Entity build() {
			return new Entity(this);
		}
	}
	private Entity(Builder b) {
		this.c = b.c;
		this.d = b.d;
		this.s = b.s;
		this.i = b.i;
	}
	
	@Override
	public int compareTo(Object o) {
		if(this == o) 
			return 0;
		if(!(o instanceof Entity))
			throw new IllegalArgumentException("Cannot compare Pair with "  
	               + o.getClass().getName());	
		Entity e = (Entity)o;
		if(i == e.i) {
			if(c == e.c) {
				if((s == null && e.s == null) || (s != null && s.compareTo(e.s) == 0)) {
					if(Double.compare(d, e.d) == 0) {
						return 0;
					} else {
						return Double.compare(d, e.d);
					}
				} else {
					if( s == null && e.s != null) return -1;
					else if( e.s == null && s != null) return 1;
					else return s.compareTo(e.s);
				}
			} else {
				return c - e.c > 0 ? 1 : -1;
			}
		} else {
			return i - e.i > 0 ? 1 : -1;
		}
	}

	@Override
	public boolean equals(Object obj) {
		if(!(obj instanceof Entity)) return false;
		Entity e = (Entity)obj;
		if(this.i == e.i)
			if(this.c == e.c) 
				if( (s == null && e.s == null) || this.s.equals(e.s))
					if(this.d == e.d) 
						return true;
		return false;
	}

	@Override
	public String toString() {
		return "[int = " + i + ",char = " + c + ",String = " + s + ", double = " + d + "]";
	}
	@Override
	public int hashCode() {
		int result = 17;
		result = 31*result + this.i;
		result = 31*result + (int)this.c;
		result = 31*result + (int)Math.round(d);
		result = 31*result + (int)s.charAt(0);
		return result ;
	}

	
}

还有测试代码：

package com.util;

import junit.framework.Assert;

import org.junit.Test;


public class TestEntity {

	@Test
	public void testEquals() {
		Entity e1 = new Entity.Builder(3).setC('b').build();
		Entity e2 = new Entity.Builder(3).setC('b').build();
		Entity e3 = new Entity.Builder(3).build();
		Integer i = Integer.valueOf("3");
		Assert.assertEquals(e1.equals(e2), true);
		Assert.assertEquals(e1.equals(e3), false);
		Assert.assertEquals(e3.equals(i), false);
	}
	@Test
	public void testCompareTo() {
		Entity e1 = new Entity.Builder(3).setC('b').build();
		Entity e2 = new Entity.Builder(3).setC('b').build();
		Entity e3 = new Entity.Builder(3).setC('a').build();
		Entity e4 = new Entity.Builder(3).setC('b').setS("asd").build();
		
		Assert.assertEquals(e1.compareTo(e1), 0);	
		Assert.assertEquals(e1.compareTo(e2), 0);
		Assert.assertEquals(e1.compareTo(e3), 1);
		Assert.assertEquals(e1.compareTo(e4), -1);
	}
	@Test(expected=IllegalArgumentException.class)
	public void testCompareTo2() {
		Entity e1 = new Entity.Builder(3).setC('b').build();
		Integer i = Integer.valueOf("3");
		Assert.assertEquals(e1.compareTo(i), 0);
	}	
}